Complex Animator Limits - not affecting positions on every frame?

Perhaps someone more skilled in Unity animations can shine a light on this but I am stuck now for days.
Please please please anyone I am going mad.

I have a fairly complex animator with lots of parameters, events, blendtrees, transitions etc. Some bones in the animation affect position and rotation, some -like wrist- only affects rotation - but in animations traditionally the position is "locked" anyway.
How does this looks in reality - Animation is playing and when I move the bone in editor it will snap to the correct animation position in the next frame.
This is how it works if the Animator has only couple of the animations, but in my complex animator, when I move the bone manually, it stays in the moved local position.

This is very problematic in situations where IK is used for example.

The crazy part is - when I delete about half of the animator, it works as supposed. Unity 2020.1

Pleeease help me someone.

 

Ok I've isolated the problem (ofc like one hour after making the post) to a singe animation file - if I have this animation in the animator (even if not connected in any way), it starts the problem. The animation is like every other animation so I don't really understand what's going on.
EDIT:
I have fixed the issue while playing in editor, but no change in build.

 

Submit a bug report. That doesn't sound like expected behaviour.

 

Ok this is crazy, it doesn't happen on friends pc, when he sends me a package it doesnt occur on mine either, when I create the same animator on my pc boom there we go again. Submitting bug report.
It happens on 2019 and 20 both....