I have just done a few interactions with the interface and it all seems normal.
Have you possibly changed the custom category while it was active for the day? That could prevent it from clearing out properly, since it would leave a question pool of 0 which could obviously crash the game.
Please try changing today's category to any of the premade ones, save, then edit the custom, crosscheck and reactivate your custom. That might help.
Edit: Just to be sure, it would probably be best if you temporarily removed the custom from your lineup entirely, i.e. from all seven days. Maybe choose difficult baseball as the stand-in, don't think many would try and play that to cheat
