Hey Jonas!
Try pulling the SD card and battery and then replace the battery. Reboot a few times and reinserted the SD card. Reopen the Gallery and Camera to make sure the settings went back to the SD card.
The normal courses of action, like wiping cache both in hardware and os modes, reapplying firmware upgrade via ODIN, pulling the battery and leaving out before reinstalling and rebooting, turning off the lock screen security, disabling proximity sensor may not work for you, but pullin the SD card and booting without might!
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