Looks like this isn’t chunk corruption at all — the stacktrace points to NaturalSpawner hanging during mob spawn checks.
A few things to try:
This is usually caused by a mob / biome / dimension mod doing something expensive or invalid during spawning. Even if you removed some big mods, configs can persist in the world — try generating a fresh test world with the same modlist to confirm.
Install a profiler (highly recommend spark) and capture a report right before / after the freeze. NaturalSpawner stalls almost always show clearly there.
Common culprits on Minecraft Java Edition 1.20.1 + Minecraft Forge 47.x:
custom mob mods
biome overhauls
structure/worldgen mods
leftover datapacks
Since it happens even solo, RAM and player count aren’t the issue. Also 16 GB is overkill — try lowering to ~8–10 GB (too much RAM can increase GC pauses).
Delete:
/world/datapacks
/world/serverconfig
then let them regenerate.
If Spark shows NaturalSpawner looping, binary-search your remaining mods (half at a time). Painful, but fastest.
Short version: this is almost certainly a spawn-related mod or datapack, not vanilla chunks.
By
Oliviia Rich ·