In the event that happens you may have to start from scratch and redownload the Wineskin wrapper from the OSX osu! tumblr (found here: ) Some of these steps initially made my game crash or stuck in an update loop. I highly recommend you back up the entire osu! folder. Osu! folder can be found by going to Show package contents > drive_c > osu! Wineskin can be found right clicking the osu! icon and clicking 'Show package contents'.
This is assuming you are using the Wineskin wrapper to run osu! on OSX. Over the course of playing osu! on OSX I've experienced multiple issues and found ways to fix them.