Skybox Reflection is broken on Mac thus some Game Objects are rendered wrongly. It includes Materials and Shadows (see attached pictures).

Steps to reproduce:
1. In Unity 5.6.0a6, create a New project
2. Add a Cube
3. Save scene and exit
4. Re-open project

Result: Cube appears as a pink object. Sometimes it appears as a green object (see attached pictures).

Note:
Mac OpenGL and Metal is affected at least (trunk rev 6ce5f2227368)
This only happens on some machines and just sometimes.