Thanks, great that you have solved this issue. Could you provide a step-by-step instruction? What did you change and how?
0. (install terminal emulator)
EDIT: as imparted by Nicholas Evans in the Fairphone support forum, BusyBox is not necessary ...
Is this a serial number ("Seriennummer") or is it a bug?
Assuming that my phone does not have the same serial nuber as yours, it is a bug since mine shows the same.