Backface Culling does not work on mobile device

I am encountering a weird problem these day that the Backface Culling does not work on some meshes. I write 'Cull Back' in my shader and it works on my PC Unity editor (both in editor mode and player mode). However, when running the game on my Android device or IOS device, some meshes appear to be rendered two-side (My mesh had faces stay close but face to opposite directions. They appeared to z-fight on my mobile device. Then I moved the camera into the mesh, and saw back faces). Does anybody have ideas?

 

Hi, I am not sure it is a bug in Unity or a bug in my code or assets.