Have you tried starting up the phone in Safe Mode
Wiping the Partition Cashe.
Just in case it's a software bug or a rouge app
I have put the process below. It's easy to do and very quick if you follow it properly
Wiping cache partition fixes some of the bugs and improve performance by removing unwanted cache files.
Turn off your phone.
Connect your phone with a USB cable
to PC or another Samsung mobile
You will see the charging icon on your screen.
Wait till it shows charging with battery percentage.
Next, press and hold the Volume up and Side key simultaneously.
You can press the volume up button just before the Side key.
The Samsung Logo followed by
Samsung Galaxy appears on the
At this point, release the keys
Phone will boot into Android Recovery mode
In Android recovery mode, using Volume keys, choose "Wipe Cache
Then press Side Key to Confirm by selecting "Yes" and then press Side Key
You get "cache wipe complete" at the
bottom of the screen
Restart the phone to complete the