How to reproduce:
1. Download MixedRealityToolkit https://github.com/Microsoft/MixedRealityToolkit-Unity and open on Unity
2. Open /Assets/HoloToolkit-Examples/Prototyping/Scenes/Primitives.unity Scene
3. Switch platform to UWP and enter Play Mode
4. Force Mixed reality device to lost boundary(close sensors with hands until controller becomes irresponsible)
5. After controller response again, try to move with joystick
6. Repeat 4-5 steps

Actual result: Project with Microsoft Mixed Reality camera sometimes has zero vertical position when start player, Sometime camera position get to real height in few seconds, sometimes not till you recalibrate Headset.

Reproduced with: 2017.2.1f1, 2017.2.2f1, 2017.3.1p3, 2018.1.0b9