Its simply the way of how your ipad may work.
There might be a way to fix this but there's no way they could fix the way the ipad works. Maybe kepp trying to reset the page so that way it can refresh everything and it may start working.
Also make sure your only clicking on where it tells you, you have notifications. If infact you are there might be a little bug the admins will have to tweak.
Also notifications are usally just a post on a thread, a private message, or a person sending you a friend request.
So just make sure to check those if you can't get into your notifications.
I also think I remember trying to click my notifications on PC and it didn't work or I just didn't click hard enough
Ill test this with my PC soon.