Suggestion: Notification Automatic Refresh
A lot of people want Duolingo to fix the notifications system. From what I've experienced, the notifications update when you refresh the page.
What I propose is that every once in a while (say every 15 seconds), the page checks for notifications (i.e. someone replying to your post). If there is a notification, the bell would ring. The whole page wouldn't refresh, though, just the notifications.