One day last week I got to my car after a day at work only to find the driver's window was halfway down. I drove to work with the windows up, and I have to hold the lock button on the fob to activate mirror folding which I definitely did. After a day at work I was pretty knackered and didn't think too much on it, was just grateful it was a dry day and I didn't have a mobile swimming pool to drive home in. Window wound up fine and stayed there.
Dropped my car off this morning for its service, no problems, but when I came to collect it the window was at halfway again. Again I didn't think too much about it as I presumed the mechanic may have put it down for whatever reason. Went to wind the window up and lo and behold, it would not stay up, dropping back to halfway as soon as it hit TDC. It would do this EVERY time I tried to close it.
First up I tried resetting the window motor, no problem at the bottom but it was simply not possible to hold it for the required five seconds at the top as it would come down immediately. VCDS showed no door controller faults.
Having spent ten minutes online looking at similar problems I thought I'd try the one thing that sorted my "wonky" BCM (definitely not working properly but no fault codes produced) when I was experimenting with LEDs earlier in the year - disconnecting the battery for five minutes.
Boom. Correct function restored and the window now stays up when it hits the top
Moral of the story? Don't overlook the simple fixes that can apply equally to any piece of technology like a computer or a smartphone before going down the rabbit hole of diagnosing electrical/electromechanical faults.