Crash occurred during server startup.
Gist with crash.

Same crash on my server as well, single player is fine.

https://gist.github.com/ProsperCraft/d3a31d3a4c3143384c964f39d7ca706c

Forge 14.23.5.2772
No sponge in my setup, so we can eliminate that.

Build 272 uploaded to fix this. Should be approved for download soon.