Wow, thanks God for this thread... Got a very similar issue on a new G21 LCi Alpina B3, thought I was going crazy. So far it happened twice within 500 miles of mileage and haven't been able to reproduce it for a video, but as soon as I manage to do so, I'll start a case with our dealer. There are A TON of M2/M3/M4s around, so I certainly hope they are already familiar with the issue...
EDIT: Got it on the video -
https://share.icloud.com/photos/028u...Klx8PakTO-9QlQ