go to safemode and observe is there same issue in safemode too if not then problem may due to other downloaded apps and if same issue in safemode then try to visit service centre and get reinstall your software update
steps to turn safemode; long press on power button> long press on power off option>click on safemode >your mobile will restart and turn into safemode.
Keep in mind that in this mode only inbuilt system app will work
I too had the same issue you cannot resolve it by resetting device.. you need to change motherboard it will cost you 9k if you are out of warranty. I personally suggest you to sell this and get a newer model.
To resolve auto restart issue please follow below given steps: Go to Settings > General management > Reset > Turn off auto start.
For further assistance, register your concern in Samsung Members Application (Open Samsung Members Application > Get help > Send Feedback > Error report/Ask questions).
