Hello, not OP but I just ran into the same crash issue on day 2 in spells class. I'm guessing any class you repeat the puzzle for gets the bug?
ETA - after reloading the game, the 2nd puzzle works but then it crashes on the 3rd day puzzle.
ETA2 - tried the herbology and astonomy/ology routes and they both work fine! It's just spells that crashes on day 2 then day 3 after reloading.