Went to the Apple store and they did diagnostics on the device and was not able to find any issues. The tech's best assessment of the cause was somehow related to the "Optimized Battery Charging" feature maybe is causing the issue when leaving it plugged into the charger extended period of time when the device is turned off. Since it happens infrequenetly under these conditions, he indicated he would pass this along to Apple engineering. A replacement offer was not extended and recommended not to turn off the device while charging. I will try to over the next month to see if it ever occurs.