Your Map Nav turned off because when your DIAD rebooted it indicated your battery was low and in power saving mode. Your battery may not have been low, but a glitch caused it to show low for a few seconds.
This!
I've had this happen multiple times with different DIADS. Battery goes from 90% to 0% for a split second causing the Navigation to turn off then the battery goes right back to 90%. There is no way to turn the Navigation back on (even restarting diad doesn't work) So I just inform management I will be very low on cradle usage for the day.