I too have an 09M8 that has the same issue, however I have found a way to reduce the effects. I see you are running a PC111 so you should be able to add fuel at 0 throttle below idle (500, 750, 1000, 1250 RPM ranges), I have found by adding fuel in this area the sled will start without issue however it takes a bit of work for the engine to respond to throttle. I have found that when this happens the AFR is usually in the 20-30:1 range and the engine is very lean. I find with the added fuel I can start the engine then flip the throttle and activate the TSS a couple of times the AFR will return to normal. I run a PCV, however I had the lean start issue right from the beginning when I bought the sled....it's more noticeable with the 925.
I also note you are running a tether, is it the old style with a rubber plug one presses on? If so maybe try a small screw in the end of the rubber plug that pushes the switch in on the tether. I've had to do this when my tether was acting up a couple of years ago....I'm in the process of replacement.
It sounds to me like you've checked everything, I understand your battle.