Or maybe not. I keep getting a service procedure interrupted message in Forscan.
It took 2 hours for the update from -UM to -UN. I turned off screen savers, power management, etc, so that the update could proceed uninterrupted.
Check if you have a screen saver running. Check if your power settings are set to change after a certain amount of time.
I use the maximum performance power mode and set everything to Never shut off or go to sleep. I also am on the AC adapter.
And.... I use a 12V battery charger attached to the 12V battery, because the car will go to sleep per se. The 12V battery charger will keep enough current available for the respective systems to stay operational when the car "sleeps". Again, its 2 hours. A sickly 12V battery could drop well below 11V after 2 hours of powering the still active systems.