Unity Animation Rigging IK Sliding/Lag/Jitter Issue SEE FIX IN DESCRIPTION
In my case, the issue came from using a humanoid avatar, and not also assigning the hand targets using OnAnimatorIK(). I made a script that manages the weight of the humanoid IK to match the weight of the Animation Rigging IK. If you need more clarification check out this doc page: https://docs.unity3d.com/ScriptRefere...
^^^ To be clear, you use the 2 systems in tandem. I'm not sure if that's the proper way to do it, but it's been working flawlessly for me for the past month