Reproduction steps:
1. Open the attached project.
2. Make sure graphics API is set to "Metal".
3. Build for iOS and open the Xcode project.
4. Rerun the application through the Xcode until it crashes ( Ussualy 1 to 5 times).
- Application crashes in "ProductName`::InvalidateState() + 64 at GfxDeviceMetal.mm:1343 [opt]"

Reproducible with:
- 5.6.0a1
- iPad Air 2 9.3.2
- iPad Mini 3 8.4.1
- iPhone SE iOS 9.3 (Lower odds to reproduce)

Not reproducible with:
- 5.5.0b10
- OpenGLES
- OSX build

Note:
Log attached in the edit