diff --git a/src/addons/calendar/services/calendar-helper.ts b/src/addons/calendar/services/calendar-helper.ts
index 593637898..80d70451f 100644
--- a/src/addons/calendar/services/calendar-helper.ts
+++ b/src/addons/calendar/services/calendar-helper.ts
@@ -546,12 +546,12 @@ export class AddonCalendarHelperProvider {
         const site = await CoreSites.getSite(siteId);
         const fetchTimestarts: number[] = [];
         const invalidateTimestarts: number[] = [];
-        const promises: Promise<unknown>[] = [];
+        let promises: Promise<unknown>[] = [];
 
         // Always fetch upcoming events.
         promises.push(AddonCalendar.getUpcomingEvents(undefined, undefined, true, site.id));
 
-        promises.concat(events.map(async (eventData) => {
+        promises = promises.concat(events.map(async (eventData) => {
 
             if (eventData.repeated <= 1) {
                 // Not repeated.
diff --git a/src/addons/mod/forum/services/handlers/prefetch.ts b/src/addons/mod/forum/services/handlers/prefetch.ts
index a9c55d2e9..79e1bf33b 100644
--- a/src/addons/mod/forum/services/handlers/prefetch.ts
+++ b/src/addons/mod/forum/services/handlers/prefetch.ts
@@ -48,13 +48,13 @@ export class AddonModForumPrefetchHandlerService extends CoreCourseActivityPrefe
         try {
             const forum = await AddonModForum.getForum(courseId, module.id);
 
-            const files = this.getIntroFilesFromInstance(module, forum);
+            let files = this.getIntroFilesFromInstance(module, forum);
 
             // Get posts.
             const posts = await this.getPostsForPrefetch(forum, { cmId: module.id });
 
             // Add posts attachments and embedded files.
-            files.concat(this.getPostsFiles(posts));
+            files = files.concat(this.getPostsFiles(posts));
 
             return files;
         } catch (error) {
diff --git a/src/addons/mod/glossary/components/index/index.ts b/src/addons/mod/glossary/components/index/index.ts
index 03be8f63b..d79b755ea 100644
--- a/src/addons/mod/glossary/components/index/index.ts
+++ b/src/addons/mod/glossary/components/index/index.ts
@@ -573,7 +573,6 @@ class AddonModGlossaryEntriesManager extends CorePageItemsListManager<EntryItem>
      */
     setOnlineEntries(onlineEntries: AddonModGlossaryEntry[], hasMoreItems: boolean = false): void {
         this.setItems((<EntryItem[]> this.offlineEntries).concat(onlineEntries), hasMoreItems);
-        this.onlineEntries.concat(onlineEntries);
     }
 
     /**
@@ -583,7 +582,6 @@ class AddonModGlossaryEntriesManager extends CorePageItemsListManager<EntryItem>
      */
     setOfflineEntries(offlineEntries: AddonModGlossaryOfflineEntry[]): void {
         this.setItems((<EntryItem[]> offlineEntries).concat(this.onlineEntries), this.hasMoreItems);
-        this.offlineEntries = offlineEntries;
     }
 
     /**
diff --git a/src/addons/notes/services/notes-sync.ts b/src/addons/notes/services/notes-sync.ts
index 2df96b2ce..a9dfac04d 100644
--- a/src/addons/notes/services/notes-sync.ts
+++ b/src/addons/notes/services/notes-sync.ts
@@ -62,12 +62,10 @@ export class AddonNotesSyncProvider extends CoreSyncBaseProvider<AddonNotesSyncR
         ]);
 
         // Get all the courses to be synced.
-        const courseIds: number[] = [];
+        let courseIds: number[] = [];
         notesArray.forEach((notes: (AddonNotesDeletedDBRecord | AddonNotesDBRecord)[]) => {
-            const courseIds = notes.map((note) => note.courseid);
-
-            courseIds.concat(courseIds);
-        }, []);
+            courseIds = courseIds.concat(notes.map((note) => note.courseid));
+        });
 
         CoreUtils.uniqueArray(courseIds);
 
diff --git a/src/core/features/mainmenu/mainmenu-tab-routing.module.ts b/src/core/features/mainmenu/mainmenu-tab-routing.module.ts
index 3a4c0ddb0..ca9c0538c 100644
--- a/src/core/features/mainmenu/mainmenu-tab-routing.module.ts
+++ b/src/core/features/mainmenu/mainmenu-tab-routing.module.ts
@@ -24,7 +24,7 @@ export function buildTabMainRoutes(injector: Injector, mainRoute: Route): Routes
 
     mainRoute.path = mainRoute.path || '';
     mainRoute.children = mainRoute.children || [];
-    mainRoute.children.concat(routes.children);
+    mainRoute.children = mainRoute.children.concat(routes.children);
 
     return [
         mainRoute,