https://pastebin.com/2nRFCw0v

I'd guess that this field is added upon generation, so upgrading to this version may be world breaking. Just a guess though. Thanks, Asie. (And, yes, there is a possibility that one of the other 113 mods is affecting this, but the call path doesn't hit anything else, and the most recent changes affect modspawning.)

Same for me and it was the only mod i updated on this time

Oh, no, that's totally my fault. And it's not world-breaking.

One thing to note, I am experiencing the same bug, but my server generated two reports.
One is the NoSuchField, and another is a "single tick took 60sec"

Problem also occurs on Client side when joining server

@asiekierka Is it related to https://github.com/asiekierka/FoamFix/blob/0.9.x-1.12.2/src/main/java/pl/asie/foamfix/coremod/injections/CachingMobSpawnerLogicInject.java#L49 ?

EDIT: From the latest commit 5f9da15 obviously

Oh and yeah I saw you pulled 0.10.4 from CurseForge, guess you know it as well

Fixed in 0.10.5.