Metallic/Smoothness texture problem on iOS vs. Standalone

Hello everyone!
I encountered a weird problem concerning the metallic/smoothness texture when building my game on an iPhone 5.

Looks like the map is totally missing, or the alpha channel isn't working.
I set the compression to RGBA PVRTC 4 bits for the mobile build.

The weird thing is, that when i try it on my iPad Air, everything looks normal.

Anybody got an idea what could be wrong here?
Attached are 2 screenshots - one from the iPhone and one from desktop:

Desktop:


iPhone 5:


Thanks in advance!

 

Nobody?