So I immediately ordered a new device from Amazon and sent the defective return.
By replacing Dakota 20, there have been no problems or crashed. The device has reliably accompanies me on my tours as a photographer and performed perfectly even at night and darkness through the mountains back to the starting point.
Ideal travel companion for me.
The only drawback: The specified time to the destination is not correct at when going on foot. I have found no setting on the speed. So the unit displays 28 minutes target, although there is a tour of 1.5 hours :-(