Had a weird thing start happening on Sunday. My 3 month old 6S+ started randomly rebooting. The screen would flash two colors very quickly, then show the Apple start screen. Varied in time - sometimes immediately on restart, sometimes after a few minutes. After a couple hours, I reset and set up as new, and while going through the set up prompts, it started again.
It settled in the morning, though it had clearly restarted goodness knows how many times overnight.
Long story short, went into Apple Sunday afternoon and they replaced the phone. There was no explanation given as to what it could have been, but I'm curious given how quick he was to go to the replacement if it's been an issue for anyone else.