Reproduction steps:
1. Open the attached project.
2. Make sure Metal graphics API is selected.
3. Build and run it for iOS.
4. Notice the picture(Screenshots attached).
5. Build it again with OpenGLES graphics API.
6. Compare the pictures.

Reproduced with:
5.5.0p4, 5.6.0p1

iPhone 7 Plus iOS 10.3 (Metal) (A10)
iPad Pro 9.7'' iOS 10.2.1 (Metal) (A9)
iPhone SE iOS 10.0.1 (Metal) (A9)

Not reproducible with:
Any device (OpenGLES 3)
iPhone 6 iOS 10.2.1 (Metal) (A8)
iPhone 6+ iOS 8.0 (Metal) (A8)
iPadMini 4 iOS 9.3.2 (Metal) (A8)
iPadAir iOS 8.1.1 (Metal) (A7)
Metal Editor