To make sure what is going on you will need to do as follow to narrow down the issue
Wipe the phone with a factory reset, without restoring anything.
If the problem persists, you got a faulty unit, that need to be serviced.
Else, restore everything.
Turn off automatic backup (to avoid destroying your backup)
Uninstall some apps
See if/that the problem persist
If it does back to 5
If it does not, you know the culprit is among the ones you knocked out last
Restore everything, end remove these apps only
You could also do it the other way r