Did you go into the gym early? If you go inside the gym before you're sent there by the quest to see Cassie, that breaks the scripts for the quest when you get to it and softlocks the game. No fix for it except to reload a save from before you went inside the gym the first time, unfortunately. (If you haven't kept back-up saves, then, welp. Start over.)
A second possibility for the bug is, when I played the game, I tried to do the janitor job at the hospital and somehow the script controlling that broke and the spots I was supposed to clean up didn't appear. I just assumed the job wasn't implemented yet and left, and this broke all the cutscenes in the game and made the gym scene softlock. Reloading to before I attempted to do the janitor job fixed the problem. I wasn't able to reproduce this bug (the job worked fine on subsequent attempts) but perhaps you ran into it too?