Filter out old migrated tasks

src/documents/views.py

@@ -879,6 +879,7 @@ class TasksViewSet(ReadOnlyModelViewSet):
     queryset = (
         PaperlessTask.objects.filter(
             acknowledged=False,
+            attempted_task__isnull=False,
         )
         .order_by("attempted_task__date_created")
         .reverse()