User session management problems
When a user's session has ended, the page still allows user actions, but then loads forever, or comes back with mysterious error messages. Here's one example (I will put in more as I come across them again):
There is no clear indication to the user that they are no longer logged in and that that is the cause of their problem—it appears that something is wrong with the system. It would be much better if the page would refresh back to the login screen once a user session has ended.