Thanks for the analysis, readiness hasn't reset and still shows all green. I am not aware DTC can get reset automatically by codes going on and off?Not if readiness isn't ready because of a past code. I had a time where I was getting ready for inspection, had passed during a long trip. Then I got a code for a short moment that cleared itself (SCR) and the readiness was reset because of that. The m57 takes forever to get readiness. Use torque on android to check obd readiness. I believe in most states you have have 1 or 2 not ready's.
The last reset was done by BMW to fix the P20ee N0x sensor code. Took about a month to trip all indicators, and just when all indicators turned green, P0671 popped up, and now off. The P0671 hasn't returned for a few days.
At least my exhaust shop is friendly and understanding and haven't charged me on the 5 revisits. Maybe I buy them a 24 pack of beer for my next round of tests?