Steps to reproduce:

1. Open attached project
2. Run the 'Test' scene in editor
3. Notice both Cube and Sphere are rendered (Cube is rendered by the camera with 'Depth' set to 0, Sphere - by the camera with 'Depth' set to 3. Both cameras have 'Clear Flags' set to 'Depth Only')
4. Build 'Test' scene for iOS
5. Deploy to an iOS device that supports Metal
6. Notice only the sphere is rendered

Notes:
This only happens on Metal. Building with GLES2/GLES3 graphics API shows both cameras, but also shows Unity Splash Screen in the background.
If you disable Anti Aliasing in Quality Settings, both cameras are rendered and the Unity Splash Screen is flickering in the background as well.

Not reproducible with: 5.2.4f1