2016 F350 6.2L gas, starting issue

This happened 3 times in 2 weeks-- twice the second time about 15 minutes apart.   Drive for 15-30 minutes,  shut off motor then come back in 10 minutes or so to restart.   All lights, radio, phone synch will work,  but engine will not turn over--no sound--almost like a security shut down.   It remote started but shut down when the key was inserted.   30 seconds later remote started again but stayed running this time with key???  Strange stuff.   Appears about 15+ minutes seems to reset the system which then allows it to start.  At dealership for 5 days but not duplicated and supposedly NO CODES at all were showing.