Reproduction Steps

launch game
wait
it freezes

Crash Report File

https://gist.github.com/papuSpartan/aca8ca501aebab166a9ad8f69a77d54d

Additional Information

loading process freezes instead of crashing.
This was after removing multiple mods which suddenly claimed to have class-loading errors.

Probably a compat issue; it was never updated to >1.16.3 when this was filed. If you haven't already, give it a try with the new build on cf.