Yes I have noticed the smell.
A BMW mechanic told me the car shouldn't be stopped (shut off the engine) when the cleaning is going on. It can make a fault code (which doesn't show up in idrive), because the pressure in the exhaust pipe before and after the particle filter is different, when the engine is shut off. I got that code while being on a road trip. I stopped to a gas station when the cleaning sequence was on. Of course I didn't know that back then but I happened to read the fault memory later and the code was there.