Unknown Error Occured

Every time I level from 71 to 72, my game freezes. After 1-3 seconds, the game kicks me to the main menu and says on the bottom left that an unknown error occurred.

I log back into my character and I'm in my hideout. No items from the map are in my inventory, the map shows that I failed it (too many deaths), and I have lost experience as if I've died.