Many iPhone, iPad, and iPod customers have experienced periodic reboots after December 2, 2017.
Apple is aware of the problem and has already issued a workaround. The issue is due to a flood of notifications for specific apps.
Apple’s workaround is to turn off notifications for the offending apps until the upgrade to the recently available iOS 11.2 can be installed.
Apple’s guidance: If your iPhone, iPad, or iPod touch unexpectedly restarts
Looking for an awesome, no-nonsense technical conference for IT Pros, Developers, and DevOps? IT/Dev Connections kicks off in Dallas, Texas in 2018!