I have the Samsung Galaxy S 8 and it randomly shuts down and reboots by itself. This seems to be a common problem with this phone. It appears that Samsung is ignoring the issue, as the problem goes back for a long time and people are still having this problem. I haven't found any response on any forums addressing this problem from Samsung. Some recommended fixes are to replace the mother board, replace the phone itself, factory reset and safe mode but apparently none of these have worked for everybody.