diff --git a/src/addon/mod/assign/providers/prefetch-handler.ts b/src/addon/mod/assign/providers/prefetch-handler.ts
index d7a86836a..93ecb3f68 100644
--- a/src/addon/mod/assign/providers/prefetch-handler.ts
+++ b/src/addon/mod/assign/providers/prefetch-handler.ts
@@ -392,7 +392,7 @@ export class AddonModAssignPrefetchHandler extends CoreCourseActivityPrefetchHan
         // Prefetch feedback.
         if (submission.feedback) {
             // Get profile and image of the grader.
-            if (submission.feedback.grade && submission.feedback.grade.grader) {
+            if (submission.feedback.grade && submission.feedback.grade.grader && submission.feedback.grade.grader != -1) {
                 userIds.push(submission.feedback.grade.grader);
             }
 
diff --git a/src/core/login/providers/helper.ts b/src/core/login/providers/helper.ts
index 9cebad238..77d06b08c 100644
--- a/src/core/login/providers/helper.ts
+++ b/src/core/login/providers/helper.ts
@@ -179,10 +179,10 @@ export class CoreLoginHelperProvider {
             } else {
                 this.goToSiteInitialPage();
             }
-        }).catch((errorMessage) => {
-            if (errorMessage) {
+        }).catch((error) => {
+            if (error) {
                 // An error occurred, display the error and logout the user.
-                this.domUtils.showErrorModal(errorMessage);
+                this.treatUserTokenError(siteData.siteUrl, error);
                 this.sitesProvider.logout();
             }
         }).finally(() => {
@@ -561,8 +561,8 @@ export class CoreLoginHelperProvider {
      * @return {boolean} True if embedded browser, false othwerise.
      */
     isSSOEmbeddedBrowser(code: number): boolean {
-        if (this.appProvider.isLinux()) {
-            // In Linux desktop apps, always use embedded browser.
+        if (this.appProvider.isLinux() || this.appProvider.isMac()) {
+            // In Linux and Mac desktop apps, always use embedded browser.
             return true;
         }
 
@@ -647,8 +647,8 @@ export class CoreLoginHelperProvider {
 
         loginUrl += '&oauthsso=' + params.id;
 
-        if (this.appProvider.isLinux()) {
-            // In Linux desktop apps, always use embedded browser.
+        if (this.appProvider.isLinux() || this.appProvider.isMac()) {
+            // In Linux and Mac desktop apps, always use embedded browser.
             this.utils.openInApp(loginUrl);
         } else {
             // Always open it in browser because the user might have the session stored in there.
diff --git a/src/core/user/providers/user.ts b/src/core/user/providers/user.ts
index 2a4d83d47..242c586d6 100644
--- a/src/core/user/providers/user.ts
+++ b/src/core/user/providers/user.ts
@@ -397,7 +397,7 @@ export class CoreUserProvider {
             userId = Number(userId); // Make sure it's a number.
 
             // Prevent repeats and errors.
-            if (!isNaN(userId) && !treated[userId]) {
+            if (!isNaN(userId) && !treated[userId] && userId > 0) {
                 treated[userId] = true;
 
                 promises.push(this.getProfile(userId, courseId, false, siteId).then((profile) => {
diff --git a/src/providers/utils/dom.ts b/src/providers/utils/dom.ts
index 05f86a032..d026def15 100644
--- a/src/providers/utils/dom.ts
+++ b/src/providers/utils/dom.ts
@@ -140,13 +140,12 @@ export class CoreDomUtilsProvider {
             const readableSize = this.textUtils.bytesToSize(size.size, 2);
 
             return this.showConfirm(this.translate.instant('core.course.confirmpartialdownloadsize', { size: readableSize }));
-        } else if (size.size >= wifiThreshold || (this.appProvider.isNetworkAccessLimited() && size.size >= limitedThreshold)) {
+        } else if (alwaysConfirm || size.size >= wifiThreshold ||
+                (this.appProvider.isNetworkAccessLimited() && size.size >= limitedThreshold)) {
             message = message || 'core.course.confirmdownload';
             const readableSize = this.textUtils.bytesToSize(size.size, 2);
 
             return this.showConfirm(this.translate.instant(message, { size: readableSize }));
-        } else if (alwaysConfirm) {
-            return this.showConfirm(this.translate.instant('core.areyousure'));
         }
 
         return Promise.resolve();