My 2018 M3 started doing this 2-3 months ago. Honestly, it's a nuthinburger when it's in your driveway, although even from 2mph I will say it's not a pleasant experience because it is completely unexpected (maddeningly random) and even at that slow speed it's a real jerk to full stop. But the other day it happened when I was on that street and *that* becomes a safety issue. I was hoping a software update would resolve it - I've taken one update since it started and no joy on a fix. I'm not wiggling, and I am no where near 135 lbs lol -- is the conclusion a bad seat belt or door sensor? It happens with seat belt on and door closed. Any chance a software update fixes this?