Same issue here. 11month old MX died without warning twice in 3 days. Seems to randomly reboot itself and come back to life. I left mine at work last night after trying to jumpstart it, just saw the notification on my phone that it came back to life at 3am. Gonna drive it home today and park it in my driveway for mobile service appointment on the 8th. Never buying a Tesla again.
That sounds like a loose cable or bad connector. When I was a mechanic I fixed several dozen of these. Ford, Chrysler, BMW, and Mercedes has issues with these. Don't ever remember having issues with a Japanese manufactured car.