Ran in to this "fun" error while playing on a server. Pastebin:
Crashy saved me from closing the game but logging back in revealed a few visual issues and I was stuck at 0-8 FPS.

Annoying. Should be a pretty easy fix though

If possible, could you check if this quick fix build fixes your problem and behaves as expected?

https://github.com/emirik0l/Golemancy/releases/tag/v1.2.3

Everything has been working perfectly since I restarted my launcher, and no one else on the server has encountered it. So I'm not sure how to replicate it

Fair enough. I'll close it for now, that fix should ensure that if it does break again it'll default to rendering golems as clay rather than crashing at least.