flip cover sensor problem

[usblaidas]

This problem exists and without the flip cover case.
My phone did that and I never had a case.

Then it is clearly magnets which make your phones go crazy. Just as @junkpod suggested, use xposed module called "magnet off", but say goodbye to compass or use any other case. What I also can suggest you is try to remove those small metal things from the flip case. Had similar problem with my old Asus Transformer so I just used a wee magnet to identify where those magnets were located and carefully with knife cut them out. After that just placed black electrical tape (it does NOT have to be electrical, it is just that it was black - same colour as case). But I am sure you guys will find a solution as the problem has been identified. Good luck!