Phone stuck in boot loop for hours and then randomly works, and repeat

I have a 6s plus and it randomly (at all different battery %s) turns off and gets stuck in a boot loop, sometimes for minutes and sometimes for hours and then after a while it boots into iOS and works fine. Sometimes it will work fine all day and sometimes only for a few mins before it starts the whole process all over again..

When it’s stuck in the loop I’ve tryed hard resetting and it has no effect.

I tried changing the battery with no resolve.. also tried updating to latest iOS (thru the phone not with iTunes)

But I’m out of ideas.. any help is much appreshiated