The dealer scanned the codes on my Z4 and according to them, the navigation reset is caused by 'interference' between the system and a connected(?) device (my phone?). That is what the BMW systems tell them the code means.
So the issue isn't with the car according to BMW.
I've had the car 6 months without any issue and suddenly it starts resetting out of the blue one weekend? Nothing changed on my phone or the car.
They could not test the issue with the mirrors going completely dark at night, so one of the techs is taking the car home with them tonight.
Please chime in if you've noticed any issues with the driver side mirror and rearview mirrors darkening at night when they shouldn't.
Rob