Bug Weird animation rigging BUG?

I created a video, I don't know what is happening here

I just followed tutorial videos, and using only the "2 bone IK"

My armature and body is under a parent object, and scaled up 100, 100, 100 (I don't know why)
Is it a probleme at all? Or what is the fix for this thing?

If I use the Model's avatar (Blake avatar, human) then this is happening...
When I select on the animator the avatar to "None" and just GENERATE GENERIC AVATAR menu, then it is working, but the character animations not working at all It is just in T pose I think, but the Rigging is working on that arm. So what is the solution for that the rigging on that arm + all others animation work together?

Something is really broken in this Animation rigging package. Unity 2019.4.0f1 animation rigging 0.2.7 preview

Thanks