When a hand looses tracking, the hand stays locked in the scene until tracked again

[SimonDarksideJ]

XRTK - Mixed Reality Toolkit Bug Report

Describe the bug

When a hand looses tracking, the hand stays locked in the scene until tracked again

To Reproduce

1. Create new XRTK project for Oculus
2. Run in standalone (via link) or on device
3. Show two hands in scene
4. Hide one hand behind back
5. See hand stuck in the scene

Expected behavior

Hand model should disappear when tracking is lost, same as controllers

Actual behavior

Hands remain until switching to controllers or hand tracking resumes