Quark 139
Forge 2781
Crashlog: https://paste.dimdev.org/ipopuyaqej.mccrash

Cross-posting from Pyre540/spawn-preventing-beacon#1

I'm also reporting here in case it is easier to solve on your end or in case it needs additional information. I'm no programmer so just covering all the bases.

Quark 140
Forge 14.23.5.2805
Crashlog: https://gist.github.com/Lorelando/9b037cf5ceab3982d13d17a6f7703a00

Looks like it is the same issue.

Setting B:"Extra potions"=false in line 827 prevents the crash on startup (as a temporary workaround).