M-a-x-G

I am trying to get to the bottom of an issue with my 2011 W221 S350 M276, which displays as follows:
Driving at any speed, forwards or reverse, accelerating or cruising, I experience random (what I perceive to be) engine shut-offs for less than one second. The engine looses power, and seems to shut-off, what happens at slow (crawling) speed.
If the speed is over 40km/h the engine is push started by the kinetic energy of the rolling car.
Most of the time the 'engine stop' occurs when accelerating for overtaking.
No error messages (DTC) are recorded.
I can drive for 100km and nothing happens, as it was the case when I dropped the car off at the dealership and they test drove it for 30km and didn't experience the engine stop.
Because the engine stop happens briefly, I cannot tell, whether the tachometer needle drops or not. I did not see any warning lights coming up in the dash either.

I have changed to a different new-ish and highly frequented brand petrol station to eliminate fuel issues.
In addition I ran the tank down to 5 litres added Methylated spirits to bind any water if present, and filled up. The car is my daily driver for a 200km round-trip, hence, sees a tank full of new petrol every 4 days.

Other than the engine stop, the car runs flawless, is being serviced per schedule, etc.

This is not related to start-stop function. What may be relevant: I got an engine software update prior to this occurring.

Considering there are no error message being recorded when the engine stop occurs, I am thinking of recording CAN C messages to see, if any signals are missing or extra ones present when this engine stop occurs.

Any hints on how to troubleshoot this would be appreciated... or hints on what to look for or record.