With eng off, your readings should drop to 0.000 AC volts.
I do not know if this makes a difference or not but after recently shutting the car off I tested the AC volts from both the battery and the Alternator and they tested at .0231 and .024 respectively.
Your cel flashing at key on engine off is normal.
If you want to try logging more I would recommend also logging maf flow, fuel rail pressure, tps voltage, throttle position absolute (actual), throttle position commanded and knock sensor activity if you can. I dont use my x3 for logging so I dont know if you can log all those functions or not. I can on Forscan Lite, which I highly recommend if you need a obd2 scanner for other vehicles.
Sadly enough my tuner (Bama Revx) does not do the things you mentioned from TPS voltage onwards. In the video Fuel Rail Pressure is bottom left.