The GUI mixin your mod is using crashes the game whenever a player opens the spin-dial gui of Effortless Building mod.

It might do you good to look at a fix Mr Crayfish's Gun Mod 1.16.5 recently pulled into their repo for the same compatibility issue. They only had to change two lines; the way they were grabbing the window instance.

crash-2021-05-04_21.39.08-client.txt