Device status says "custom"? Can no longer download certain apps

[AC Question]

Alright I'm not really sure what happened here but my phone is no longer certified with Google Play and now the device status says "custom" and shows the word on the screen while booting up, complete with an unlocked padlock symbol. I only just noticed this when trying to play Fire Emblem: Heroes, only to get endless errors. I uninstalled it and as I went to reinstall it said it wasn't compatible with my device. After a lot of google searches I figure this may be part of the issue? Pokemon Go doesn't seem to be working now either. I didn't root it, so I'm not sure what happened? I'd appreciate any help. It's really frustrating. The phone is a Samsung Galaxy s4.