Originally Posted by TriX5

Michel, welcome!

Upon re-reading your post it seems like a wiring break. Since you only get this problem in motion. This will be tough to find but some scouting might show where work has been done on the loom or maybe from installation of aftermarket electronics.

The other things that come to mind, make sure your ground connections are tight. Some of the items you mention are governed by the GM module, windows, wipers. GM modules are cheap and could be worth trying a swap.

As to help, the only good BMW indy I know about is in the north, Autohuis Buursema in Leek. If you are near there, you might try them, they seem capable.