Jasper are you in PHX as well?
20 times is insane. i've seen where one tech claimed it was a loose pin. To me (as a software engineer) there is specific reasons that 'Warning' would come up and shut the the entire drivetrain. It should be fairly easy to pin down WHAT is tripping it as, well, it's software and there are things called logs, written when software freaks out. Even if the powertrain is handled by MS (frightening) they love to write logs. Finding a 'tech' that can sift through code, that might be much harder.
I've also seen the 12v battery blamed. Easy enough to claim but for those who are able to restart the car a few minutes later it can't go from 3volts to enough to start the car unless the HV battery charges it in that wait state, which I read isn't happening unless the car is left 'idle' in park, running.
The loose plug, or possibly the braking regen system (that oddly no one has seemed to question, though a lot, not all but a lot of these SSNs, happen after stopping, possibly coasting). I'd almost put my money on the "clunk" that develops after 1000 or 2000 miles from the engine/trans/whatever is causing it, might be pulling a plug loose or severing a ground or weakening a constant voltage line somewhere. The pot hole/rough road theory is another vibration / thing loosening possibility.
I live in PHX where the roads I drive (in Chandler) are really quite smooth, not so much in the rest of PHX really.
If it's ECM or PTM reflashing I really want to know what version it's on and if I have the new one.