Been having these same issues with my car since I bought it in 2016. My symptoms were somewhat mild and was more annoying than anything. So I had the SIB update and installed PPK1. It got better, but soon returned. During this time I also installed the BMS intake. Afterwards, I had two "limp mode" situations and got the following codes:
2DCE - Valvetronic System no adjustment possible
2EOF - Valvetronic System deactivated adj fault too frequent
It was 18 months between incidents.
My SA said I eventually need to replace the eccentric shaft actuator.
Then I read that the BMS intake may be exacerbating the problem, so I removed it and put my factory intake back on and the symptoms have reduced significantly. I still get some mild fluctuations in RPM when I come to a stop and an occasional "stumble", but the issues are still there.
So I did some reading on the valvetronic system issues with the N55 and came across the following:
N55 Failing VANOS Solenoid Symptoms:
•Loss of Power and Torque
•Engine hesitation and bogging
•Rough idle, bouncing RPM’s
•Starting issues and potential stalling of vehicle
•Limp mode
https://www.bmwn55tuning.com/n55-common-problems/
So my question, could the real culprit be my eccentric shaft actuator failing?
Looking at replacing it and seeing what happens.