I saw your post and wanted to add to the knowledge base on this problem if possible.
My wife's 2015 x5 35i xdrive M-sport experienced exactly the same problem, casually driving to work (< 3miles), then all the sudden transmission malfunction. Fortunately she was able to coast downhill into a parking area and get safely off the road.
The x5 has ~99k miles, has a GA8HP45Z ZF transmission. Towed vehicle to BWM Mastertech Indy shop. Indy shop found the same code I did (421342, which is the same as one of your codes). I could clear the code, but once I start the vehicle, it would immediately come back. The transmission is stuck in park. The vehicle also had 420341 code (Gear-ratio monitoring...), but I was able to clear that code and it didn't return (probably because the vehicle is un-drivable and there is nothing to monitor). The Indy shop sent me the attached pics from ZF on the failure. (the middle pic indicates a sheered off ring in one of the gearing mechanisms, so much for a robust transmission as is claimed by ZF).
There's a youtube video on the ZF 8HP transmission tear down (explains how the 8HP works) by John Kelly of the Automotive Technology Department - Transmission Lab @ Weber State if your interested in learning more about this transmission. Link is here:
Hope this helps in understanding the problem. Needless to say, I'm not happy about it. Never had a BMW transmission do such a thing before. This car is babied too!
