diff --git a/src/queries.ts b/src/queries.ts
index 10b51e6d8..08f6e9799 100644
--- a/src/queries.ts
+++ b/src/queries.ts
@@ -70,6 +70,11 @@ interface DesktopQueryParams extends BaseQueryParams {
 
 interface AndroidQueryParams extends BaseQueryParams {
   bid_android: string;
+  /** True when the bucket is an aw-import-screentime (iOS) bucket.
+   *  ScreenTime events carry a "title" key; aw-watcher-android events do not.
+   *  Keep false (the default) for regular Android watcher buckets so that
+   *  merge_events_by_keys does not drop every event due to a missing key. */
+  isIos?: boolean;
 }
 
 interface MultiQueryParams extends BaseQueryParams {
@@ -154,8 +159,17 @@ export function canonicalEvents(params: DesktopQueryParams | AndroidQueryParams)
   return [
     // Fetch window/app events
     `events = flood(${queryBucket(bid_window)});`,
-    // On Android, merge events to avoid overload of events
-    isAndroidParams(params) ? 'events = merge_events_by_keys(events, ["app", "title"]);' : '',
+    // On Android, merge events to avoid overload of events.
+    // aw-watcher-android events carry "app"/"package"/"classname" but NOT "title";
+    // merge_events_by_keys drops events missing any requested key, so including
+    // "title" here collapses all Android watcher events to zero duration
+    // (regression introduced in bf0fc84 to support iOS ScreenTime, which DOES
+    // carry "title").  Only add "title" when the bucket is an iOS ScreenTime import.
+    isAndroidParams(params)
+      ? params.isIos
+        ? 'events = merge_events_by_keys(events, ["app", "title"]);'
+        : 'events = merge_events_by_keys(events, ["app"]);'
+      : '',
     // Fetch not-afk events
     isDesktopParams(params)
       ? `not_afk = flood(${queryBucket(params.bid_afk)});
@@ -225,19 +239,25 @@ const default_limit = 100; // Hardcoded limit per group
 export function appQuery(
   appbucket: string,
   categories: Category[],
-  filter_categories: string[][]
+  filter_categories: string[][],
+  isIos = false
 ): string[] {
   appbucket = escape_doublequote(appbucket);
   const params: AndroidQueryParams = {
     bid_android: appbucket,
     categories,
     filter_categories,
+    isIos,
   };
 
+  // aw-watcher-android events have no "title" key; only ScreenTime (iOS) does.
+  // Merging on "title" when it is absent drops every event (see canonicalEvents).
+  const titleMergeKeys = isIos ? '["app", "classname", "title"]' : '["app", "classname"]';
+
   const code = `
     ${canonicalEvents(params)}
 
-    title_events = sort_by_duration(merge_events_by_keys(events, ["app", "classname", "title"]));
+    title_events = sort_by_duration(merge_events_by_keys(events, ${titleMergeKeys}));
     app_events   = sort_by_duration(merge_events_by_keys(title_events, ["app"]));
     cat_events   = sort_by_duration(merge_events_by_keys(events, ["$category"]));
 
diff --git a/src/stores/activity.ts b/src/stores/activity.ts
index c9816ae17..3ab694cc7 100644
--- a/src/stores/activity.ts
+++ b/src/stores/activity.ts
@@ -328,16 +328,15 @@ export const useActivityStore = defineStore('activity', {
       );
       const selectedBucket = iosBucket || this.buckets.android[0];
 
+      const isIos = !!iosBucket;
       const q = queries.appQuery(
         selectedBucket,
         categoryStore.classes_for_query,
-        filter_categories
+        filter_categories,
+        isIos
       );
       const data = await getClient().query(periods, q).catch(this.errorHandler);
 
-      // Post-process for iOS compatibility (swap app <-> title)
-      const isIos = !!iosBucket;
-
       if (isIos && data && data[0] && data[0].title_events) {
         // Build bundle ID → human name lookup from title_events before modifying them.
         // title_events has 'app' = bundle ID and 'title' = human-readable name.
@@ -551,10 +550,14 @@ export const useActivityStore = defineStore('activity', {
         }
 
         // Prefer ScreenTime bucket over Android watcher for consistency with query_android
-        const iosOrAndroidBucket =
-          this.buckets.android.find((id: string) => id.startsWith('aw-import-screentime')) ||
-          this.buckets.android[0];
+        const iosBucketForCategory = this.buckets.android.find((id: string) =>
+          id.startsWith('aw-import-screentime')
+        );
+        const iosOrAndroidBucket = iosBucketForCategory || this.buckets.android[0];
         const isAndroid = iosOrAndroidBucket !== undefined;
+        // ScreenTime (iOS) buckets carry a "title" key; aw-watcher-android buckets do not.
+        // Pass isIos so canonicalEvents uses the correct merge keys and titles are preserved.
+        const isIosForCategory = !!iosBucketForCategory;
         const categories = useCategoryStore().classes_for_query;
         // TODO: Clean up call, pass QueryParams in fullDesktopQuery as well
         // TODO: Unify QueryOptions and QueryParams
@@ -571,6 +574,7 @@ export const useActivityStore = defineStore('activity', {
           ...(isAndroid
             ? {
                 bid_android: iosOrAndroidBucket,
+                isIos: isIosForCategory,
               }
             : {
                 bid_afk: this.buckets.afk[0],
diff --git a/src/views/settings/CategoryBuilder.vue b/src/views/settings/CategoryBuilder.vue
index 77d25a9b4..8c04ae0e1 100644
--- a/src/views/settings/CategoryBuilder.vue
+++ b/src/views/settings/CategoryBuilder.vue
@@ -261,7 +261,12 @@ export default {
       let bucketParams;
       if (!windowAvail && androidBuckets.length > 0) {
         const screentimeBucket = androidBuckets.find(id => id.startsWith('aw-import-screentime'));
-        bucketParams = { bid_android: screentimeBucket || androidBuckets[0] };
+        bucketParams = {
+          bid_android: screentimeBucket || androidBuckets[0],
+          // ScreenTime (iOS) events carry a "title" key; aw-watcher-android events do not.
+          // Pass isIos so canonicalEvents uses the correct merge keys and titles are preserved.
+          isIos: !!screentimeBucket,
+        };
       } else {
         bucketParams = {
           bid_window: 'aw-watcher-window_' + hostname,
diff --git a/test/unit/queries.test.node.ts b/test/unit/queries.test.node.ts
index 9b15c23ef..0947b1a28 100644
--- a/test/unit/queries.test.node.ts
+++ b/test/unit/queries.test.node.ts
@@ -55,7 +55,7 @@
  *             (Flatpak app ID retained: 'one.ablaze.floorp')
  */
 
-import { browser_appname_regex, querystr_to_array } from '~/queries';
+import { browser_appname_regex, appQuery, categoryQuery, querystr_to_array } from '~/queries';
 
 // Convert ActivityWatch (?i) patterns to JS RegExp with i flag for testing.
 // AW server uses Python-style (?i) inline flag; JS uses RegExp 'i' flag instead.
@@ -277,3 +277,63 @@ describe('querystr_to_array', () => {
     expect(result).toHaveLength(2);
   });
 });
+
+// Regression guard for ActivityWatch/aw-webui#959:
+// aw-watcher-android events carry "app"/"package"/"classname" but NOT "title".
+// merge_events_by_keys skips events missing any requested key, so including
+// "title" in the Android (non-iOS) path collapsed all activity to 0s.
+describe('appQuery merge key regression', () => {
+  const categories: any[] = [];
+  const filter_categories: string[][] = [];
+
+  test('Android watcher path does NOT merge on "title"', () => {
+    const q = appQuery('aw-watcher-android_device', categories, filter_categories, false);
+    const joined = q.join('\n');
+    // The canonical-events step must not reference "title" for the non-iOS path
+    expect(joined).not.toContain('merge_events_by_keys(events, ["app", "title"])');
+    // The title_events step must merge on "classname" but not "title"
+    expect(joined).toContain('"app", "classname"');
+    expect(joined).not.toContain('"app", "classname", "title"');
+  });
+
+  test('iOS ScreenTime path DOES merge on "title"', () => {
+    const q = appQuery('aw-import-screentime_device', categories, filter_categories, true);
+    const joined = q.join('\n');
+    // The canonical-events step must reference "title" for the iOS path
+    expect(joined).toContain('merge_events_by_keys(events, ["app", "title"])');
+    // The title_events step must merge on "title" for iOS
+    expect(joined).toContain('"app", "classname", "title"');
+  });
+});
+
+// Regression guard for the category/Category-Builder ScreenTime caller paths:
+// query_category_time_by_period and CategoryBuilder.vue both call categoryQuery/
+// canonicalEvents with bid_android.  They were missing isIos, causing ScreenTime
+// buckets to lose title distinctions before category assignment.
+describe('categoryQuery merge key regression (ScreenTime callers)', () => {
+  const categories: any[] = [];
+  const filter_categories: string[][] = [];
+
+  test('Android watcher bucket does NOT merge on "title" in category query', () => {
+    const q = categoryQuery({
+      bid_android: 'aw-watcher-android_device',
+      categories,
+      filter_categories,
+      filter_afk: false,
+    });
+    const joined = q.join('\n');
+    expect(joined).not.toContain('merge_events_by_keys(events, ["app", "title"])');
+  });
+
+  test('iOS ScreenTime bucket DOES merge on "title" in category query when isIos=true', () => {
+    const q = categoryQuery({
+      bid_android: 'aw-import-screentime_device',
+      isIos: true,
+      categories,
+      filter_categories,
+      filter_afk: false,
+    });
+    const joined = q.join('\n');
+    expect(joined).toContain('merge_events_by_keys(events, ["app", "title"])');
+  });
+});