I made an avatar that switches in-between the default prone animation and a custom animation, in VRChat, the legs crumple up so I used the Animator Tracking Control component to change the control for the legs to animation.
However. This doesn't work unless you also set head-tracking to animation. Which of course a problem when you want head tracking.
I'm not 100% sure, but this does not feel like a user-issue, rather a VRC-issue as it isn't really the intended behavior you expect when using this component.
I've attached numerous images showing my setup and the problem faced.