Describe the bug
I wrote a bug report for the mod Incontrol. You might be interested in it too, because it's related to your mod too. - McJtyMods/InControl#336

Steps To Reproduce
Steps to reproduce the behavior:
"With some chance the game crashes or stops (no crash report) when trying to block untamedwilds spawns. After removing the limit of 10 pieces per chunk, the game stopped stopping. Crashes occurred not regularly, but with some chance, when moving quickly through the not yet explored parts of the map. More details in the crash report." (c)

Crash Log
crash-2022-07-17_17.03.27-server (1).txt

Version (please complete the following information):
The crash report lists all of these things.

I have a feeling that even the datapack your animals are ignoring. I set the values for catfish extremely low, but they still show up as many as before. When I set the weight to 0 and the group size to 0 it doesn't work either. A new world was created to test.

Dragon Play.zip

Modpack - https://www.curseforge.com/minecraft/modpacks/play-as-dragon

when trying to block untamedwilds spawns

You won't be able to do that through 3rd party tools, since I spawn the mobs outside of how vanilla does it
You have a few workarounds:

• Disable the "masterSpawner" config option so none of UntamedWilds mobs spawn, and have InControl (or other mods) manage the whole thing (there may be issues, but it should properly assigns variants to the correct places)
• If available, set the freq values in the config to zero to disable certain categories (not recommended, since I will probably change that in a future version)
• Disable certain UntamedWilds variants through a datapack, so there's no mobs that could spawn (may need a bunch of extra work to not break things)
• Disable certain UntamedWilds mobs from spawning through a datapack

Disabling mobs through a datapack is experimental, but it works as far as I have tested, and have no plans on changing the format in the short term, so editing it should be safe. Attached is a small datapack that exposes the internal spawn lists, since the whole thing is experimental, any change in those files overrides the internal files, so removing entries effectively disables their spawns in certain categories:

untamedwilds_spawns.zip

Oh, I could do it all, but I think it would be easier for me to wait for an update. I'm already a month into the modpack, and I don't want to spend even more time and effort on something that will most likely break in the next update. The creatures from your mod are involved in about 40 quests related to animal protection. I'm doing this with the support of the Russian Biological Society. Everything is already balanced and I'm more likely to break it all rather than fix it myself.

There are only a few mobs that bother me a lot. First and foremost are the big clams, trevally and catfish. They often appear more than 80-150 units in the loading zone (the rest of the mobs of 3-20). I will edit and add a datapack for testing. I hope this solves the problem.