Does it overheat as well?
To rule out any 3rd party apps or customisations that might be causing your issues, please boot to Safe Mode.
To get to Safe Mode - Long press Power button, long press Power off icon, tap Safe mode icon. (When booted into Safe mode you may need to turn off flight mode as it sometimes enables itself). Monitor your devices behaviour. If the issue is fixed, then you know it's one of your 3rd party apps or customisations that were the culprit. It's up to you to determine which one it is by a process of elimination.
