Welcome to Android Central! You can tell if the phone is rooted by running
Root Checker.
Try booting into Safe Mode, which temporarily disables all 3rd party apps. These steps should work:
https://forums.androidcentral.com/e?...token=Y_JDP6lb
If the problem disappears in Safe Mode, then something you installed is causing the problem. You may have to uninstall apps one by one until the problem disappears. If the problem persists in Safe Mode, then it's more likely to be a hardware or firmware problem.