It is a large modpack and for the time being I disabled this feature as a quick fix, maybe later I will have time to find the mod causing this.

EDIT: It is on 1.18.2

I think it's Improved Mobs? I've had this issue before when stealth was still part of PWD, and somebody reported that improved mobs has a mob x-ray feature that causes this.

Thats not in the modpack, but it gave me an idea what it could be.
I will test it later, but its gonna take some time since I have 300 mods in the pack.