The mod animations were smooth the whole time until I lit a Immersive Portal after that they were choppy and really laggy for some reason, everything else is rendering fine.

Also when I checked the log it spammed:

[01:00:55] [Render thread/ERROR]: ########## GL ERROR ##########
[01:00:55] [Render thread/ERROR]: @ Render
[01:00:55] [Render thread/ERROR]: 65539: Invalid key -1

Log: latest.log

EDIT: Disabling "Animation smoothing" seems to mostly fix the issue.

Then Immersive Portal seems to break the player tick logic. Will have to look into it.