diff --git a/src/app/+collection-page/collection-page.component.ts b/src/app/+collection-page/collection-page.component.ts
index a390bda4cb..026b78bd10 100644
--- a/src/app/+collection-page/collection-page.component.ts
+++ b/src/app/+collection-page/collection-page.component.ts
@@ -1,7 +1,7 @@
 import { ChangeDetectionStrategy, Component, OnInit } from '@angular/core';
 import { ActivatedRoute, Router } from '@angular/router';
-import { BehaviorSubject, of as observableOf, Observable, Subject } from 'rxjs';
-import { filter, flatMap, map, startWith, switchMap, take, tap } from 'rxjs/operators';
+import { BehaviorSubject, Observable, Subject } from 'rxjs';
+import { filter, map, mergeMap, startWith, switchMap, take } from 'rxjs/operators';
 import { PaginatedSearchOptions } from '../shared/search/paginated-search-options.model';
 import { SearchService } from '../core/shared/search/search.service';
 import { SortDirection, SortOptions } from '../core/cache/models/sort-options.model';
@@ -15,14 +15,10 @@ import { Bitstream } from '../core/shared/bitstream.model';
 import { Collection } from '../core/shared/collection.model';
 import { DSpaceObjectType } from '../core/shared/dspace-object-type.model';
 import { Item } from '../core/shared/item.model';
-import {
-  getSucceededRemoteData,
-  redirectOn404Or401,
-  toDSpaceObjectListRD
-} from '../core/shared/operators';
+import { getSucceededRemoteData, redirectOn404Or401, toDSpaceObjectListRD } from '../core/shared/operators';
 
 import { fadeIn, fadeInOut } from '../shared/animations/fade';
-import { hasNoValue, hasValue, isNotEmpty } from '../shared/empty.util';
+import { hasValue, isNotEmpty } from '../shared/empty.util';
 import { PaginationComponentOptions } from '../shared/pagination/pagination-component-options.model';
 
 @Component({
@@ -69,7 +65,7 @@ export class CollectionPageComponent implements OnInit {
     this.logoRD$ = this.collectionRD$.pipe(
       map((rd: RemoteData<Collection>) => rd.payload),
       filter((collection: Collection) => hasValue(collection)),
-      flatMap((collection: Collection) => collection.logo)
+      mergeMap((collection: Collection) => collection.logo)
     );
 
     this.paginationChanges$ = new BehaviorSubject({
diff --git a/src/app/+item-page/edit-item-page/item-authorizations/item-authorizations.component.ts b/src/app/+item-page/edit-item-page/item-authorizations/item-authorizations.component.ts
index 8153990a02..26d4e19a16 100644
--- a/src/app/+item-page/edit-item-page/item-authorizations/item-authorizations.component.ts
+++ b/src/app/+item-page/edit-item-page/item-authorizations/item-authorizations.component.ts
@@ -2,7 +2,7 @@ import { Component, OnDestroy, OnInit } from '@angular/core';
 import { ActivatedRoute } from '@angular/router';
 
 import { BehaviorSubject, Observable, of as observableOf, Subscription } from 'rxjs';
-import { catchError, filter, first, flatMap, map, take } from 'rxjs/operators';
+import { catchError, filter, first, map, mergeMap, take } from 'rxjs/operators';
 
 import { PaginatedList } from '../../../core/data/paginated-list';
 import {
@@ -85,7 +85,7 @@ export class ItemAuthorizationsComponent implements OnInit, OnDestroy {
 
     const bundles$: Observable<PaginatedList<Bundle>> = this.item$.pipe(
       filter((item: Item) => isNotEmpty(item.bundles)),
-      flatMap((item: Item) => item.bundles),
+      mergeMap((item: Item) => item.bundles),
       getFirstSucceededRemoteDataWithNotEmptyPayload(),
       catchError((error) => {
         console.error(error);
@@ -102,7 +102,7 @@ export class ItemAuthorizationsComponent implements OnInit, OnDestroy {
       }),
       bundles$.pipe(
         take(1),
-        flatMap((list: PaginatedList<Bundle>) => list.page),
+        mergeMap((list: PaginatedList<Bundle>) => list.page),
         map((bundle: Bundle) => ({ id: bundle.id, bitstreams: this.getBundleBitstreams(bundle) }))
       ).subscribe((entry: BundleBitstreamsMapEntry) => {
         this.bundleBitstreamsMap.set(entry.id, entry.bitstreams)
diff --git a/src/app/+item-page/simple/item-types/shared/item-relationships-utils.ts b/src/app/+item-page/simple/item-types/shared/item-relationships-utils.ts
index 6ef035f1e6..5d895a9920 100644
--- a/src/app/+item-page/simple/item-types/shared/item-relationships-utils.ts
+++ b/src/app/+item-page/simple/item-types/shared/item-relationships-utils.ts
@@ -1,6 +1,6 @@
 import { combineLatest as observableCombineLatest, zip as observableZip } from 'rxjs';
 import { Observable } from 'rxjs/internal/Observable';
-import { distinctUntilChanged, flatMap, map, switchMap } from 'rxjs/operators';
+import { distinctUntilChanged, map, mergeMap, switchMap } from 'rxjs/operators';
 import { PaginatedList } from '../../../../core/data/paginated-list';
 import { RemoteData } from '../../../../core/data/remote-data';
 import { Relationship } from '../../../../core/shared/item-relationships/relationship.model';
@@ -43,7 +43,7 @@ export const compareArraysUsingIds = <T extends { id: string }>() =>
 export const relationsToItems = (thisId: string) =>
   (source: Observable<Relationship[]>): Observable<Item[]> =>
     source.pipe(
-      flatMap((rels: Relationship[]) =>
+      mergeMap((rels: Relationship[]) =>
         observableZip(
           ...rels.map((rel: Relationship) => observableCombineLatest(rel.leftItem, rel.rightItem))
         )
diff --git a/src/app/community-list-page/community-list-service.ts b/src/app/community-list-page/community-list-service.ts
index 4699e6faaa..81dfae57fa 100644
--- a/src/app/community-list-page/community-list-service.ts
+++ b/src/app/community-list-page/community-list-service.ts
@@ -5,7 +5,7 @@ import { Observable, of as observableOf } from 'rxjs';
 import { AppState } from '../app.reducer';
 import { CommunityDataService } from '../core/data/community-data.service';
 import { FindListOptions } from '../core/data/request.models';
-import { map, flatMap } from 'rxjs/operators';
+import { map, mergeMap } from 'rxjs/operators';
 import { Community } from '../core/shared/community.model';
 import { Collection } from '../core/shared/collection.model';
 import { getSucceededRemoteData } from '../core/shared/operators';
@@ -127,6 +127,7 @@ export class CommunityListService {
 
   /**
    * Gets all top communities, limited by page, and transforms this in a list of flatNodes.
+   * @param findOptions       FindListOptions
    * @param expandedNodes     List of expanded nodes; if a node is not expanded its subCommunities and collections need
    *                            not be added to the list
    */
@@ -148,7 +149,7 @@ export class CommunityListService {
         return new PaginatedList(newPageInfo, newPage);
       })
     );
-    return topComs$.pipe(flatMap((topComs: PaginatedList<Community>) => this.transformListOfCommunities(topComs, 0, null, expandedNodes)));
+    return topComs$.pipe(mergeMap((topComs: PaginatedList<Community>) => this.transformListOfCommunities(topComs, 0, null, expandedNodes)));
   };
 
   /**
@@ -229,7 +230,7 @@ export class CommunityListService {
         })
           .pipe(
             getSucceededRemoteData(),
-            flatMap((rd: RemoteData<PaginatedList<Community>>) =>
+            mergeMap((rd: RemoteData<PaginatedList<Community>>) =>
               this.transformListOfCommunities(rd.payload, level + 1, communityFlatNode, expandedNodes))
           );
 
diff --git a/src/app/core/data/request.effects.ts b/src/app/core/data/request.effects.ts
index 44d8416f35..196dcf18c8 100644
--- a/src/app/core/data/request.effects.ts
+++ b/src/app/core/data/request.effects.ts
@@ -1,7 +1,7 @@
-import { Inject, Injectable, Injector } from '@angular/core';
+import { Injectable, Injector } from '@angular/core';
 import { Actions, Effect, ofType } from '@ngrx/effects';
 import { Observable, of as observableOf } from 'rxjs';
-import { catchError, filter, flatMap, map, take } from 'rxjs/operators';
+import { catchError, filter, map, mergeMap, take } from 'rxjs/operators';
 
 import { hasValue, isNotEmpty } from '../../shared/empty.util';
 import { StoreActionTypes } from '../../store.actions';
@@ -11,7 +11,12 @@ import { DSpaceRESTV2Response } from '../dspace-rest-v2/dspace-rest-v2-response.
 
 import { DSpaceRESTv2Service } from '../dspace-rest-v2/dspace-rest-v2.service';
 import { DSpaceSerializer } from '../dspace-rest-v2/dspace.serializer';
-import { RequestActionTypes, RequestCompleteAction, RequestExecuteAction, ResetResponseTimestampsAction } from './request.actions';
+import {
+  RequestActionTypes,
+  RequestCompleteAction,
+  RequestExecuteAction,
+  ResetResponseTimestampsAction
+} from './request.actions';
 import { RequestError, RestRequest } from './request.models';
 import { RequestEntry } from './request.reducer';
 import { RequestService } from './request.service';
@@ -29,14 +34,14 @@ export class RequestEffects {
 
   @Effect() execute = this.actions$.pipe(
     ofType(RequestActionTypes.EXECUTE),
-    flatMap((action: RequestExecuteAction) => {
+    mergeMap((action: RequestExecuteAction) => {
       return this.requestService.getByUUID(action.payload).pipe(
         take(1)
       );
     }),
     filter((entry: RequestEntry) => hasValue(entry)),
     map((entry: RequestEntry) => entry.request),
-    flatMap((request: RestRequest) => {
+    mergeMap((request: RestRequest) => {
       let body = request.body;
       if (isNotEmpty(request.body) && !request.isMultipart) {
         const serializer = new DSpaceSerializer(getClassForType(request.body.type));
diff --git a/src/app/core/json-patch/json-patch-operations.service.ts b/src/app/core/json-patch/json-patch-operations.service.ts
index c1b37bf904..5cd4abb8d1 100644
--- a/src/app/core/json-patch/json-patch-operations.service.ts
+++ b/src/app/core/json-patch/json-patch-operations.service.ts
@@ -1,5 +1,5 @@
 import { merge as observableMerge, Observable, throwError as observableThrowError } from 'rxjs';
-import { distinctUntilChanged, filter, find, flatMap, map, partition, take, tap } from 'rxjs/operators';
+import { distinctUntilChanged, filter, find, map, mergeMap, partition, take, tap } from 'rxjs/operators';
 import { Store } from '@ngrx/store';
 
 import { hasValue, isEmpty, isNotEmpty, isNotUndefined, isUndefined } from '../../shared/empty.util';
@@ -45,7 +45,7 @@ export abstract class JsonPatchOperationsService<ResponseDefinitionDomain, Patch
     const requestId = this.requestService.generateRequestId();
     let startTransactionTime = null;
     const [patchRequest$, emptyRequest$] = partition((request: PatchRequestDefinition) => isNotEmpty(request.body))(hrefObs.pipe(
-      flatMap((endpointURL: string) => {
+      mergeMap((endpointURL: string) => {
         return this.store.select(jsonPatchOperationsByResourceType(resourceType)).pipe(
           take(1),
           filter((operationsList: JsonPatchOperationsResourceEntry) => isUndefined(operationsList) || !(operationsList.commitPending)),
@@ -84,7 +84,7 @@ export abstract class JsonPatchOperationsService<ResponseDefinitionDomain, Patch
         filter((request: PatchRequestDefinition) => isNotEmpty(request.body)),
         tap(() => this.store.dispatch(new StartTransactionPatchOperationsAction(resourceType, resourceId, startTransactionTime))),
         tap((request: PatchRequestDefinition) => this.requestService.configure(request)),
-        flatMap(() => {
+        mergeMap(() => {
           const [successResponse$, errorResponse$] = partition((response: RestResponse) => response.isSuccessful)(this.requestService.getByUUID(requestId).pipe(
             getResponseFromEntry(),
             find((entry: RestResponse) => startTransactionTime < entry.timeAdded),
@@ -93,7 +93,7 @@ export abstract class JsonPatchOperationsService<ResponseDefinitionDomain, Patch
           return observableMerge(
             errorResponse$.pipe(
               tap(() => this.store.dispatch(new RollbacktPatchOperationsAction(resourceType, resourceId))),
-              flatMap((error: ErrorResponse) => observableThrowError(error))),
+              mergeMap((error: ErrorResponse) => observableThrowError(error))),
             successResponse$.pipe(
               filter((response: PostPatchSuccessResponse) => isNotEmpty(response)),
               tap(() => this.store.dispatch(new CommitPatchOperationsAction(resourceType, resourceId))),
diff --git a/src/app/core/locale/locale.service.ts b/src/app/core/locale/locale.service.ts
index 315fc02833..74822e7185 100644
--- a/src/app/core/locale/locale.service.ts
+++ b/src/app/core/locale/locale.service.ts
@@ -1,4 +1,4 @@
-import { Injectable, Inject } from '@angular/core';
+import { Inject, Injectable } from '@angular/core';
 
 import { TranslateService } from '@ngx-translate/core';
 
@@ -6,9 +6,9 @@ import { isEmpty, isNotEmpty } from '../../shared/empty.util';
 import { CookieService } from '../services/cookie.service';
 import { environment } from '../../../environments/environment';
 import { AuthService } from '../auth/auth.service';
-import { Observable, of as observableOf, combineLatest } from 'rxjs';
-import { map, take, flatMap } from 'rxjs/operators';
-import { NativeWindowService, NativeWindowRef } from '../services/window.service';
+import { combineLatest, Observable, of as observableOf } from 'rxjs';
+import { map, mergeMap, take } from 'rxjs/operators';
+import { NativeWindowRef, NativeWindowService } from '../services/window.service';
 
 export const LANG_COOKIE = 'dsLanguage';
 
@@ -74,7 +74,7 @@ export class LocaleService {
 
     return obs$.pipe(
       take(1),
-      flatMap(([isAuthenticated, isLoaded]) => {
+      mergeMap(([isAuthenticated, isLoaded]) => {
         // TODO to enabled again when https://github.com/DSpace/dspace-angular/issues/739 will be resolved
         const epersonLang$: Observable<string[]> = observableOf([]);
 /*        if (isAuthenticated && isLoaded) {
diff --git a/src/app/core/locale/server-locale.service.ts b/src/app/core/locale/server-locale.service.ts
index b33338240f..2385840145 100644
--- a/src/app/core/locale/server-locale.service.ts
+++ b/src/app/core/locale/server-locale.service.ts
@@ -1,8 +1,8 @@
-import { LocaleService, LANG_ORIGIN } from './locale.service';
+import { LANG_ORIGIN, LocaleService } from './locale.service';
 import { Injectable } from '@angular/core';
-import { Observable, combineLatest, of as observableOf } from 'rxjs';
-import { take, flatMap, map } from 'rxjs/operators';
-import { isNotEmpty, isEmpty } from 'src/app/shared/empty.util';
+import { combineLatest, Observable, of as observableOf } from 'rxjs';
+import { map, mergeMap, take } from 'rxjs/operators';
+import { isEmpty, isNotEmpty } from 'src/app/shared/empty.util';
 
 @Injectable()
 export class ServerLocaleService extends LocaleService {
@@ -20,7 +20,7 @@ export class ServerLocaleService extends LocaleService {
 
     return obs$.pipe(
       take(1),
-      flatMap(([isAuthenticated, isLoaded]) => {
+      mergeMap(([isAuthenticated, isLoaded]) => {
         let epersonLang$: Observable<string[]> = observableOf([]);
         if (isAuthenticated && isLoaded) {
           epersonLang$ = this.authService.getAuthenticatedUserFromStore().pipe(
diff --git a/src/app/core/registry/registry.service.ts b/src/app/core/registry/registry.service.ts
index f349cf428c..c1a4dd9594 100644
--- a/src/app/core/registry/registry.service.ts
+++ b/src/app/core/registry/registry.service.ts
@@ -21,7 +21,7 @@ import {
   MetadataRegistrySelectFieldAction,
   MetadataRegistrySelectSchemaAction
 } from '../../+admin/admin-registries/metadata-registry/metadata-registry.actions';
-import { flatMap, map, tap } from 'rxjs/operators';
+import { map, mergeMap, tap } from 'rxjs/operators';
 import { NotificationsService } from '../../shared/notifications/notifications.service';
 import { TranslateService } from '@ngx-translate/core';
 import { MetadataSchema } from '../metadata/metadata-schema.model';
@@ -75,7 +75,7 @@ export class RegistryService {
       map((schemas: PaginatedList<MetadataSchema>) => schemas.page),
       isNotEmptyOperator(),
       map((schemas: MetadataSchema[]) => schemas.filter((schema) => schema.prefix === prefix)[0]),
-      flatMap((schema: MetadataSchema) => this.metadataSchemaService.findById(`${schema.id}`, ...linksToFollow))
+      mergeMap((schema: MetadataSchema) => this.metadataSchemaService.findById(`${schema.id}`, ...linksToFollow))
     );
   }
 
@@ -290,6 +290,8 @@ export class RegistryService {
    * Retrieve a filtered paginated list of metadata fields
    * @param query {string} The query to use for the metadata field name, can be part of the fully qualified field,
    * should start with the start of the schema, element or qualifier (e.g. “dc.ti”, “contributor”, “auth”, “contributor.ot”)
+   * @param options
+   * @param linksToFollow
    * @returns an observable that emits a remote data object with a page of metadata fields that match the query
    */
   queryMetadataFields(query: string, options: FindListOptions = {}, ...linksToFollow: Array<FollowLinkConfig<MetadataField>>): Observable<RemoteData<PaginatedList<MetadataField>>> {
diff --git a/src/app/core/shared/operators.ts b/src/app/core/shared/operators.ts
index 29e41907e1..aeb475b47f 100644
--- a/src/app/core/shared/operators.ts
+++ b/src/app/core/shared/operators.ts
@@ -1,6 +1,6 @@
 import { Router, UrlTree } from '@angular/router';
-import { Observable, combineLatest as observableCombineLatest } from 'rxjs';
-import { filter, find, flatMap, map, switchMap, take, tap } from 'rxjs/operators';
+import { combineLatest as observableCombineLatest, Observable } from 'rxjs';
+import { filter, find, map, mergeMap, switchMap, take, tap } from 'rxjs/operators';
 import { hasValue, hasValueOperator, isNotEmpty } from '../../shared/empty.util';
 import { SearchResult } from '../../shared/search/search-result.model';
 import { DSOSuccessResponse, RestResponse } from '../cache/response.models';
@@ -23,14 +23,14 @@ import { getEndUserAgreementPath } from '../../info/info-routing-paths';
 export const getRequestFromRequestHref = (requestService: RequestService) =>
   (source: Observable<string>): Observable<RequestEntry> =>
     source.pipe(
-      flatMap((href: string) => requestService.getByHref(href)),
+      mergeMap((href: string) => requestService.getByHref(href)),
       hasValueOperator()
     );
 
 export const getRequestFromRequestUUID = (requestService: RequestService) =>
   (source: Observable<string>): Observable<RequestEntry> =>
     source.pipe(
-      flatMap((uuid: string) => requestService.getByUUID(uuid)),
+      mergeMap((uuid: string) => requestService.getByUUID(uuid)),
       hasValueOperator()
     );
 
diff --git a/src/app/core/submission/submission-rest.service.ts b/src/app/core/submission/submission-rest.service.ts
index 350874bc50..981ce1c5da 100644
--- a/src/app/core/submission/submission-rest.service.ts
+++ b/src/app/core/submission/submission-rest.service.ts
@@ -1,12 +1,12 @@
 import { Injectable } from '@angular/core';
 
 import { merge as observableMerge, Observable, throwError as observableThrowError } from 'rxjs';
-import { distinctUntilChanged, filter, flatMap, map, mergeMap, tap } from 'rxjs/operators';
+import { distinctUntilChanged, filter, map, mergeMap, tap } from 'rxjs/operators';
 
 import { RequestService } from '../data/request.service';
 import { isNotEmpty } from '../../shared/empty.util';
 import {
-  DeleteRequest, GetRequest,
+  DeleteRequest,
   PostRequest,
   RestRequest,
   SubmissionDeleteRequest,
@@ -20,7 +20,7 @@ import { HALEndpointService } from '../shared/hal-endpoint.service';
 import { RemoteDataBuildService } from '../cache/builders/remote-data-build.service';
 import { ErrorResponse, RestResponse, SubmissionSuccessResponse } from '../cache/response.models';
 import { getResponseFromEntry } from '../shared/operators';
-import {URLCombiner} from '../url-combiner/url-combiner';
+import { URLCombiner } from '../url-combiner/url-combiner';
 
 /**
  * The service handling all submission REST requests
@@ -96,7 +96,7 @@ export class SubmissionRestService {
       map((endpointURL: string) => this.getEndpointByIDHref(endpointURL, scopeId)),
       map((endpointURL: string) => new SubmissionDeleteRequest(requestId, endpointURL)),
       tap((request: DeleteRequest) => this.requestService.configure(request)),
-      flatMap(() => this.fetchRequest(requestId)),
+      mergeMap(() => this.fetchRequest(requestId)),
       distinctUntilChanged());
   }
 
@@ -121,7 +121,7 @@ export class SubmissionRestService {
         this.requestService.removeByHrefSubstring(request.href);
         this.requestService.configure(request);
       }),
-      flatMap(() => this.fetchRequest(requestId)),
+      mergeMap(() => this.fetchRequest(requestId)),
       distinctUntilChanged());
   }
 
@@ -149,7 +149,7 @@ export class SubmissionRestService {
       distinctUntilChanged(),
       map((endpointURL: string) => new SubmissionPostRequest(requestId, endpointURL, body, options)),
       tap((request: PostRequest) => this.requestService.configure(request)),
-      flatMap(() => this.fetchRequest(requestId)),
+      mergeMap(() => this.fetchRequest(requestId)),
       distinctUntilChanged());
   }
 
@@ -173,7 +173,7 @@ export class SubmissionRestService {
       distinctUntilChanged(),
       map((endpointURL: string) => new SubmissionPatchRequest(requestId, endpointURL, body)),
       tap((request: PostRequest) => this.requestService.configure(request)),
-      flatMap(() => this.fetchRequest(requestId)),
+      mergeMap(() => this.fetchRequest(requestId)),
       distinctUntilChanged());
   }
 
diff --git a/src/app/core/submission/vocabularies/vocabulary.service.ts b/src/app/core/submission/vocabularies/vocabulary.service.ts
index 595edfc861..f76877dba4 100644
--- a/src/app/core/submission/vocabularies/vocabulary.service.ts
+++ b/src/app/core/submission/vocabularies/vocabulary.service.ts
@@ -3,7 +3,7 @@ import { HttpClient } from '@angular/common/http';
 
 import { Store } from '@ngrx/store';
 import { Observable } from 'rxjs';
-import { distinctUntilChanged, first, flatMap, map } from 'rxjs/operators';
+import { distinctUntilChanged, map, mergeMap } from 'rxjs/operators';
 
 import { FollowLinkConfig } from '../../../shared/utils/follow-link-config.model';
 import { dataService } from '../../cache/builders/build-decorators';
@@ -22,7 +22,7 @@ import { PaginatedList } from '../../data/paginated-list';
 import { Vocabulary } from './models/vocabulary.model';
 import { VOCABULARY } from './models/vocabularies.resource-type';
 import { VocabularyEntry } from './models/vocabulary-entry.model';
-import { hasValue, isNotEmpty, isNotEmptyOperator } from '../../../shared/empty.util';
+import { isNotEmpty, isNotEmptyOperator } from '../../../shared/empty.util';
 import {
   configureRequest,
   filterSuccessfulResponses,
@@ -295,7 +295,7 @@ export class VocabularyService {
 
     return this.vocabularyEntryDetailDataService.getBrowseEndpoint().pipe(
       map((href: string) => `${href}/${linkPath}`),
-      flatMap((href) => this.vocabularyEntryDetailDataService.findByHref(href, ...linksToFollow))
+      mergeMap((href) => this.vocabularyEntryDetailDataService.findByHref(href, ...linksToFollow))
     );
   }
 
@@ -320,7 +320,7 @@ export class VocabularyService {
       pageInfo.currentPage
     );
     return this.vocabularyEntryDetailDataService.getFindAllHref(options, linkPath).pipe(
-      flatMap((href) => this.vocabularyEntryDetailDataService.findAllByHref(href, options, ...linksToFollow))
+      mergeMap((href) => this.vocabularyEntryDetailDataService.findAllByHref(href, options, ...linksToFollow))
     );
   }
 
diff --git a/src/app/core/tasks/tasks.service.ts b/src/app/core/tasks/tasks.service.ts
index 0eae88e96c..fbc108d765 100644
--- a/src/app/core/tasks/tasks.service.ts
+++ b/src/app/core/tasks/tasks.service.ts
@@ -1,10 +1,10 @@
 import { HttpHeaders } from '@angular/common/http';
 
 import { merge as observableMerge, Observable, of as observableOf } from 'rxjs';
-import { distinctUntilChanged, filter, flatMap, map, mergeMap, tap } from 'rxjs/operators';
+import { distinctUntilChanged, filter, map, mergeMap, tap } from 'rxjs/operators';
 
 import { DataService } from '../data/data.service';
-import { DeleteRequest, FindListOptions, PostRequest, TaskDeleteRequest, TaskPostRequest } from '../data/request.models';
+import { DeleteRequest, PostRequest, TaskDeleteRequest, TaskPostRequest } from '../data/request.models';
 import { isNotEmpty } from '../../shared/empty.util';
 import { HttpOptions } from '../dspace-rest-v2/dspace-rest-v2.service';
 import { ProcessTaskResponse } from './models/process-task-response';
@@ -80,7 +80,7 @@ export abstract class TasksService<T extends CacheableObject> extends DataServic
       distinctUntilChanged(),
       map((endpointURL: string) => new TaskPostRequest(requestId, endpointURL, body, options)),
       tap((request: PostRequest) => this.requestService.configure(request)),
-      flatMap((request: PostRequest) => this.fetchRequest(requestId)),
+      mergeMap((request: PostRequest) => this.fetchRequest(requestId)),
       distinctUntilChanged());
   }
 
@@ -104,7 +104,7 @@ export abstract class TasksService<T extends CacheableObject> extends DataServic
       map((endpointURL: string) => this.getEndpointByIDHref(endpointURL, scopeId)),
       map((endpointURL: string) => new TaskDeleteRequest(requestId, endpointURL, null, options)),
       tap((request: DeleteRequest) => this.requestService.configure(request)),
-      flatMap((request: DeleteRequest) => this.fetchRequest(requestId)),
+      mergeMap((request: DeleteRequest) => this.fetchRequest(requestId)),
       distinctUntilChanged());
   }
 
diff --git a/src/app/shared/form/builder/ds-dynamic-form-ui/models/relation-group/dynamic-relation-group.components.ts b/src/app/shared/form/builder/ds-dynamic-form-ui/models/relation-group/dynamic-relation-group.components.ts
index 1198803bd8..68115289da 100644
--- a/src/app/shared/form/builder/ds-dynamic-form-ui/models/relation-group/dynamic-relation-group.components.ts
+++ b/src/app/shared/form/builder/ds-dynamic-form-ui/models/relation-group/dynamic-relation-group.components.ts
@@ -2,7 +2,7 @@ import { ChangeDetectorRef, Component, EventEmitter, Input, OnDestroy, OnInit, O
 import { FormGroup } from '@angular/forms';
 
 import { combineLatest, Observable, of as observableOf, Subscription } from 'rxjs';
-import { filter, flatMap, map, mergeMap, scan } from 'rxjs/operators';
+import { filter, map, mergeMap, scan } from 'rxjs/operators';
 import {
   DynamicFormControlComponent,
   DynamicFormControlModel,
@@ -13,7 +13,7 @@ import {
 } from '@ng-dynamic-forms/core';
 import { isEqual, isObject } from 'lodash';
 
-import { DynamicRelationGroupModel} from './dynamic-relation-group.model';
+import { DynamicRelationGroupModel } from './dynamic-relation-group.model';
 import { FormBuilderService } from '../../../form-builder.service';
 import { SubmissionFormsModel } from '../../../../../../core/config/models/config-submission-forms.model';
 import { FormService } from '../../../../form.service';
@@ -226,7 +226,7 @@ export class DsDynamicRelationGroupComponent extends DynamicFormControlComponent
 
       // If authority
       this.subs.push(initChipsValue$.pipe(
-        flatMap((valueModel) => {
+        mergeMap((valueModel) => {
           const returnList: Array<Observable<any>> = [];
           valueModel.forEach((valueObj) => {
             const returnObj = Object.keys(valueObj).map((fieldName) => {
diff --git a/src/app/shared/object-collection/shared/mydspace-item-submitter/item-submitter.component.ts b/src/app/shared/object-collection/shared/mydspace-item-submitter/item-submitter.component.ts
index 01c0dd9f35..61087b3851 100644
--- a/src/app/shared/object-collection/shared/mydspace-item-submitter/item-submitter.component.ts
+++ b/src/app/shared/object-collection/shared/mydspace-item-submitter/item-submitter.component.ts
@@ -1,7 +1,7 @@
 import { Component, Input, OnInit } from '@angular/core';
 
 import { Observable } from 'rxjs';
-import { filter, find, flatMap, map } from 'rxjs/operators';
+import { filter, find, map, mergeMap } from 'rxjs/operators';
 
 import { EPerson } from '../../../../core/eperson/models/eperson.model';
 import { RemoteData } from '../../../../core/data/remote-data';
@@ -34,7 +34,7 @@ export class ItemSubmitterComponent implements OnInit {
   ngOnInit() {
     this.submitter$ = (this.object.workflowitem as Observable<RemoteData<WorkflowItem>>).pipe(
       filter((rd: RemoteData<WorkflowItem>) => (rd.hasSucceeded && isNotUndefined(rd.payload))),
-      flatMap((rd: RemoteData<WorkflowItem>) => rd.payload.submitter as Observable<RemoteData<EPerson>>),
+      mergeMap((rd: RemoteData<WorkflowItem>) => rd.payload.submitter as Observable<RemoteData<EPerson>>),
       find((rd: RemoteData<EPerson>) => rd.hasSucceeded && isNotEmpty(rd.payload)),
       map((rd: RemoteData<EPerson>) => rd.payload));
   }
diff --git a/src/app/shared/vocabulary-treeview/vocabulary-treeview.service.ts b/src/app/shared/vocabulary-treeview/vocabulary-treeview.service.ts
index dd58a6aede..8677326603 100644
--- a/src/app/shared/vocabulary-treeview/vocabulary-treeview.service.ts
+++ b/src/app/shared/vocabulary-treeview/vocabulary-treeview.service.ts
@@ -1,7 +1,7 @@
 import { Injectable } from '@angular/core';
 
 import { BehaviorSubject, Observable, of as observableOf } from 'rxjs';
-import { flatMap, map, merge, scan } from 'rxjs/operators';
+import { map, merge, mergeMap, scan } from 'rxjs/operators';
 import { findIndex } from 'lodash';
 
 import { LOAD_MORE_NODE, LOAD_MORE_ROOT_NODE, TreeviewFlatNode, TreeviewNode } from './vocabulary-treeview-node.model';
@@ -186,13 +186,13 @@ export class VocabularyTreeviewService {
 
     this.vocabularyService.getVocabularyEntriesByValue(query, false, this.vocabularyOptions, new PageInfo()).pipe(
       getFirstSucceededRemoteListPayload(),
-      flatMap((result: VocabularyEntry[]) => (result.length > 0) ? result : observableOf(null)),
-      flatMap((entry: VocabularyEntry) =>
+      mergeMap((result: VocabularyEntry[]) => (result.length > 0) ? result : observableOf(null)),
+      mergeMap((entry: VocabularyEntry) =>
         this.vocabularyService.findEntryDetailById(entry.otherInformation.id, this.vocabularyName).pipe(
           getFirstSucceededRemoteDataPayload()
         )
       ),
-      flatMap((entry: VocabularyEntryDetail) => this.getNodeHierarchy(entry)),
+      mergeMap((entry: VocabularyEntryDetail) => this.getNodeHierarchy(entry)),
       scan((acc: TreeviewNode[], value: TreeviewNode) => {
         if (isEmpty(value) || findIndex(acc, (node) => node.item.otherInformation.id === value.item.otherInformation.id) !== -1) {
           return acc;
@@ -256,7 +256,7 @@ export class VocabularyTreeviewService {
    */
   private getNodeHierarchyById(id: string): Observable<string[]> {
     return this.getById(id).pipe(
-      flatMap((entry: VocabularyEntryDetail) => this.getNodeHierarchy(entry, [], false)),
+      mergeMap((entry: VocabularyEntryDetail) => this.getNodeHierarchy(entry, [], false)),
       map((node: TreeviewNode) => this.getNodeHierarchyIds(node))
     );
   }
@@ -349,7 +349,7 @@ export class VocabularyTreeviewService {
 
     if (node.item.hasOtherInformation() && isNotEmpty(node.item.otherInformation.parent)) {
       return this.getParentNode(node.item.otherInformation.id).pipe(
-        flatMap((parentItem: VocabularyEntryDetail) => this.getNodeHierarchy(parentItem, [node], toStore))
+        mergeMap((parentItem: VocabularyEntryDetail) => this.getNodeHierarchy(parentItem, [node], toStore))
       )
     } else {
       return observableOf(node);
diff --git a/src/app/submission/import-external/submission-import-external.component.ts b/src/app/submission/import-external/submission-import-external.component.ts
index d28186a703..9a34b4f8e5 100644
--- a/src/app/submission/import-external/submission-import-external.component.ts
+++ b/src/app/submission/import-external/submission-import-external.component.ts
@@ -2,7 +2,7 @@ import { Component, OnDestroy, OnInit } from '@angular/core';
 import { Router } from '@angular/router';
 
 import { BehaviorSubject, combineLatest, Subscription } from 'rxjs';
-import { filter, flatMap, take } from 'rxjs/operators';
+import { filter, mergeMap, take } from 'rxjs/operators';
 import { NgbModal, NgbModalRef } from '@ng-bootstrap/ng-bootstrap';
 
 import { ExternalSourceService } from '../../core/data/external-source.service';
@@ -179,7 +179,7 @@ export class SubmissionImportExternalComponent implements OnInit, OnDestroy {
         this.searchConfigService.paginatedSearchOptions.pipe(
           filter((searchOptions) => searchOptions.query === query),
           take(1),
-          flatMap((searchOptions) => this.externalService.getExternalSourceEntries(this.routeData.sourceId, searchOptions).pipe(
+          mergeMap((searchOptions) => this.externalService.getExternalSourceEntries(this.routeData.sourceId, searchOptions).pipe(
             getFinishedRemoteData(),
             take(1)
           )),
diff --git a/src/app/submission/sections/form/section-form.component.ts b/src/app/submission/sections/form/section-form.component.ts
index 7372cd2a5d..39a94848cf 100644
--- a/src/app/submission/sections/form/section-form.component.ts
+++ b/src/app/submission/sections/form/section-form.component.ts
@@ -2,7 +2,7 @@ import { ChangeDetectorRef, Component, Inject, ViewChild } from '@angular/core';
 import { DynamicFormControlEvent, DynamicFormControlModel } from '@ng-dynamic-forms/core';
 
 import { combineLatest as observableCombineLatest, Observable, Subscription } from 'rxjs';
-import { distinctUntilChanged, filter, find, flatMap, map, switchMap, take, tap } from 'rxjs/operators';
+import { distinctUntilChanged, filter, find, map, mergeMap, switchMap, take, tap } from 'rxjs/operators';
 import { TranslateService } from '@ngx-translate/core';
 import { isEqual } from 'lodash';
 
@@ -158,8 +158,8 @@ export class SubmissionSectionformComponent extends SectionModelComponent {
     this.formConfigService.getConfigByHref(this.sectionData.config).pipe(
       map((configData: ConfigData) => configData.payload),
       tap((config: SubmissionFormsModel) => this.formConfig = config),
-      flatMap(() =>
-        observableCombineLatest(
+      mergeMap(() =>
+        observableCombineLatest([
           this.sectionService.getSectionData(this.submissionId, this.sectionData.id, this.sectionData.sectionType),
           this.submissionObjectService.getHrefByID(this.submissionId).pipe(take(1)).pipe(
             switchMap((href: string) => {
@@ -174,7 +174,7 @@ export class SubmissionSectionformComponent extends SectionModelComponent {
                 switchMap(() => this.submissionObjectService.findById(this.submissionId, followLink('item')).pipe(getSucceededRemoteData(), getRemoteDataPayload()) as Observable<SubmissionObject>)
               )
             })
-          )
+          )]
         )),
       take(1))
       .subscribe(([sectionData, workspaceItem]: [WorkspaceitemSectionFormObject, WorkspaceItem]) => {
diff --git a/src/app/submission/sections/license/section-license.component.ts b/src/app/submission/sections/license/section-license.component.ts
index 00af9f9774..5dbd20a726 100644
--- a/src/app/submission/sections/license/section-license.component.ts
+++ b/src/app/submission/sections/license/section-license.component.ts
@@ -7,7 +7,7 @@ import {
 } from '@ng-dynamic-forms/core';
 
 import { Observable, Subscription } from 'rxjs';
-import { distinctUntilChanged, filter, find, flatMap, map, startWith, take } from 'rxjs/operators';
+import { distinctUntilChanged, filter, find, map, mergeMap, startWith, take } from 'rxjs/operators';
 import { CollectionDataService } from '../../../core/data/collection-data.service';
 import { RemoteData } from '../../../core/data/remote-data';
 import { JsonPatchOperationPathCombiner } from '../../../core/json-patch/builder/json-patch-operation-path-combiner';
@@ -131,7 +131,7 @@ export class SubmissionSectionLicenseComponent extends SectionModelComponent {
 
     this.licenseText$ = this.collectionDataService.findById(this.collectionId, followLink('license')).pipe(
       filter((collectionData: RemoteData<Collection>) => isNotUndefined((collectionData.payload))),
-      flatMap((collectionData: RemoteData<Collection>) => (collectionData.payload as any).license),
+      mergeMap((collectionData: RemoteData<Collection>) => (collectionData.payload as any).license),
       find((licenseData: RemoteData<License>) => isNotUndefined((licenseData.payload))),
       map((licenseData: RemoteData<License>) => licenseData.payload.text),
       startWith(''));
diff --git a/src/app/submission/sections/upload/file/section-upload-file.component.ts b/src/app/submission/sections/upload/file/section-upload-file.component.ts
index 9923c358e7..209bd8e991 100644
--- a/src/app/submission/sections/upload/file/section-upload-file.component.ts
+++ b/src/app/submission/sections/upload/file/section-upload-file.component.ts
@@ -1,7 +1,7 @@
 import { ChangeDetectorRef, Component, Input, OnChanges, OnInit, ViewChild } from '@angular/core';
 
 import { BehaviorSubject, Subscription } from 'rxjs';
-import { filter, first, flatMap, take } from 'rxjs/operators';
+import { filter, first, mergeMap, take } from 'rxjs/operators';
 import { DynamicFormControlModel, } from '@ng-dynamic-forms/core';
 import { NgbModal } from '@ng-bootstrap/ng-bootstrap';
 
@@ -250,9 +250,9 @@ export class SubmissionSectionUploadFileComponent implements OnChanges, OnInit {
     this.subscriptions.push(this.formService.isValid(this.formId).pipe(
       take(1),
       filter((isValid) => isValid),
-      flatMap(() => this.formService.getFormData(this.formId)),
+      mergeMap(() => this.formService.getFormData(this.formId)),
       take(1),
-      flatMap((formData: any) => {
+      mergeMap((formData: any) => {
         // collect bitstream metadata
         Object.keys((formData.metadata))
           .filter((key) => isNotEmpty(formData.metadata[key]))
diff --git a/src/app/submission/sections/upload/section-upload.component.ts b/src/app/submission/sections/upload/section-upload.component.ts
index f25a859631..4e45a67383 100644
--- a/src/app/submission/sections/upload/section-upload.component.ts
+++ b/src/app/submission/sections/upload/section-upload.component.ts
@@ -1,7 +1,7 @@
 import { ChangeDetectorRef, Component, Inject } from '@angular/core';
 
 import { BehaviorSubject, combineLatest as observableCombineLatest, Observable, Subscription } from 'rxjs';
-import { distinctUntilChanged, filter, find, flatMap, map, reduce, take, tap } from 'rxjs/operators';
+import { distinctUntilChanged, filter, find, map, mergeMap, reduce, take, tap } from 'rxjs/operators';
 
 import { SectionModelComponent } from '../models/section.model';
 import { hasValue, isNotEmpty, isNotUndefined, isUndefined } from '../../../shared/empty.util';
@@ -159,11 +159,11 @@ export class SubmissionSectionUploadComponent extends SectionModelComponent {
         filter((submissionObject: SubmissionObjectEntry) => isNotUndefined(submissionObject) && !submissionObject.isLoading),
         filter((submissionObject: SubmissionObjectEntry) => isUndefined(this.collectionId) || this.collectionId !== submissionObject.collection),
         tap((submissionObject: SubmissionObjectEntry) => this.collectionId = submissionObject.collection),
-        flatMap((submissionObject: SubmissionObjectEntry) => this.collectionDataService.findById(submissionObject.collection)),
+        mergeMap((submissionObject: SubmissionObjectEntry) => this.collectionDataService.findById(submissionObject.collection)),
         filter((rd: RemoteData<Collection>) => isNotUndefined((rd.payload))),
         tap((collectionRemoteData: RemoteData<Collection>) => this.collectionName = collectionRemoteData.payload.name),
         // TODO review this part when https://github.com/DSpace/dspace-angular/issues/575 is resolved
-/*        flatMap((collectionRemoteData: RemoteData<Collection>) => {
+/*        mergeMap((collectionRemoteData: RemoteData<Collection>) => {
           return this.resourcePolicyService.findByHref(
             (collectionRemoteData.payload as any)._links.defaultAccessConditions.href
           );
@@ -176,8 +176,8 @@ export class SubmissionSectionUploadComponent extends SectionModelComponent {
               ? defaultAccessConditionsRemoteData.payload : [defaultAccessConditionsRemoteData.payload];
           }
         }),*/
-        flatMap(() => config$),
-        flatMap((config: SubmissionUploadsModel) => {
+        mergeMap(() => config$),
+        mergeMap((config: SubmissionUploadsModel) => {
           this.required$.next(config.required);
           this.availableAccessConditionOptions = isNotEmpty(config.accessConditionOptions) ? config.accessConditionOptions : [];
 
@@ -203,7 +203,7 @@ export class SubmissionSectionUploadComponent extends SectionModelComponent {
                 mapGroups$.push(
                   this.groupService.findById(accessCondition.selectGroupUUID).pipe(
                     find((rd: RemoteData<Group>) => !rd.isResponsePending && rd.hasSucceeded),
-                    flatMap((group: RemoteData<Group>) => group.payload.subgroups),
+                    mergeMap((group: RemoteData<Group>) => group.payload.subgroups),
                     find((rd: RemoteData<PaginatedList<Group>>) => !rd.isResponsePending && rd.hasSucceeded),
                     map((rd: RemoteData<PaginatedList<Group>>) => ({
                       accessCondition: accessCondition.name,
@@ -215,7 +215,7 @@ export class SubmissionSectionUploadComponent extends SectionModelComponent {
           });
           return mapGroups$;
         }),
-        flatMap((entry) => entry),
+        mergeMap((entry) => entry),
         reduce((acc: any[], entry: AccessConditionGroupsMapEntry) => {
           acc.push(entry);
           return acc;