Just for added confirmation, my 2015 M135i was having the same issue when cold starting. It was getting so bad that it was nearly stalling 90% of the time when starting from cold but started normal when hot.
So, after commuting home, I turned off the engine and unplugged the MAF sensor, restarted the car and left it idling for 10 minutes. It might've been in my head but I straightaway thought the car felt more smooth at idle for those 10 minutes.
I have now started the car when cold 3 times, and each time it has been faultless. No stutter, no drop in revs, a nice cold start sound from the exhaust
Many thanks to who suggested the fix, really does seem to work!