Hello there.

Sadly, I'm experiencing a CTD when it turns night. This happens after reloading the save too. After removing this mod this CTD does not happen again.
Crash Report:
https://pastebin.com/DUbCcJMM

Regards

This seems to be a compatibility issue with the mod "zombietactics2: Zombie Tactics 2 2.0.8+1.21.4" you have installed.

The description for that mod shows that the version for 1.21.4 will not be maintained and updated anymore.
Also Zombie Tactics 2 seems to be a fork of the mod Zombie Tactics, which states:
"Warning! Zombie Tactics makes significant changes to zombie AI, and thus, may be wholly incompatible with other AI-changing mods." This is probably the root of the problem.

I ran a quick test with the newer version of Zombie Tactics 2 for Minecraft 1.21.5 and I didn't see any crashes.
So it really seems to be an issue with the old / unsupported version of Zombie Tactics 2 for Minecraft 1.21.4.

Yes that is the case. I don't understand how I could overlook this obvious mod when I looked them over before writing this report. Normally I'd have removed all mods I'd expect to conflict myself for testing. I'm sorry. Thank you for your time.

No problem, glad I could help :)