Vanilla Mobs don't render their animations. They move around with their models frozen. I've noticed it for Zombies, Skeletons, (Also Cave) Spiders, and Vindicators. Not sure about other mobs. I have not tested with modded mobs. I have attempted to re-add their animations with the config, but it changes nothing.

If anything, I'd like to know how to disable the mob animations.

If you need any more info, just ask.

Update: Figured out the problem. It was the mod Performant. For anyone else who has this issue, within the config for Performant, make sure the setting eventLoadBalancing = false. It is located under the heading ["Load balancing settings". "Event load balancing settings"]. It is the second section.

I will close this thread now.