Mystery bone jittering

I’m using Blender, for rigging used Auto Rig Pro 3.60. I exported my character with animations, also seperatly exported hair rig. In Ue4 (4.26.1) i parented my hair rig to the head bone. When playing animation my hair jitters, also parented my point light to the head bone:jitter1

In Blender head bone have one key and its constant:jitter2

Moreover, i tested in FBX Review, animations perfect, this means its not fails in export. I checked transformations in UE4 animation, and its weird. Head Bone is always running, only the rotation, this is the reason of the jitter, but as i said in blender i had one keyframe, is it works like that? -Then why on other bones(cheek, teeth, nose etc) its stays constant? Also my skull bones are running:
jitter3

My skeleton tree:

In Asset Detail of animation clip, i found this tab “Compression” if i change “Compression Error Threshold Scale” to 0, jitter become weaker, but there is still some:


But after, whole animation is weird and janky. Don’t touch it.

I have pretty good Simplify Factor on export animation: 0.05, and on import i’m usin default settings. How can i solve this problem?

Lets GOOOOO. EASY!!! SHEEEEEEEEEEEESH! AUTO RIG PRO AUTHOR IS GOD!!!
JUST DOWNLOAD NEW VERSION, UNCHECK SKULLS AND CHECK IN EXPORT FIX ROTATION! IT ADDS INVISIBLE JITTER TO THE BONES TO PREVENT ISSUES! SHEEEEESH.!!! don’t flag this post.

There’s a bug in blender where scaling of bones introduces random jitter and rotations of other bones in the chain.

It could be that’s what is happening here.