Mobs become ticking entities in latest version. Removing the mob(s) listed in the crash report doesn't resolve the issue, as spawning another mob causes it to immediately crash in the same way.
crash-2022-01-09_15.36.37-server.txt

Mobs have always been ticking entities, since they were introduced to Minecraft.

This crash is the same as #240, caused by a developer bug in Chisel and Bits 1.2.68 which has since been fixed by the developer in 1.2.69+

I guess Chisels and Bits has been having a ton of issues on ATM6 and now ATM7. For now we have the mod removed until the pack and the mod are more stable.