I ran into a situation where prone/crouching animations broke, and remained broken until changing worlds. Sample video: https://www.youtube.com/watch?v=iK0kp3v4feY
I suspect (but have not yet verified) that this was caused by the Animator Set View component, locking the viewpoint so that avatar animations cannot force the viewpoint to the ground. This brings multiple bugs to mind:
  1. I had attempted to use Set View to move the viewpoint as the avatar scaled, by scaling the avatar root with a radial puppet control, then invoking Animator Set View when the puppet control was closed. However, my viewpoint did not actually change (bug 1?)
  2. After this change, desktop crouch/prone animations broke (bug 2?)
  3. This broken state was carried over after subsequent avatar changes (this is the biggest issue here).
Note that both SDK2 and 3 avatars were affected to an extent - with SDK2 avatars, the animation was correct but the viewpoint was too high.
Rejoining the instance fixes the issue.