In my case, when I got into the car at the store, the car stayed in the "Car is off". When I put my foot on the brakes and tried to get the car to turn on (go into Park, or switch into Drive), nothing would happen. However, when I did not have my foot on the brakes, it would flash the error on the display saying I need to have my foot on the brakes to change into drive. So it was recognizing that the brakes were depressed, but just would not do anything. The service rep on the phone walked me through resets, which I had already tried, but to no avail. One of the resets caused my GPS to show me in California at Tesla HQ (I'm actually in Phoenix), so when trying to do Roadside through the app, it said it wasn't available in that area and it showed the car at Tesla HQ in Palo Alto as well. Two hours later, the first tow truck guy also could not get it into Drive, and experienced the same issue, however could not get the MX onto his flatbed and had to schedule a "four wheel lift", which wouldn't be until 5am the next morning. I got a call at 7am from the next tow truck guy asking me to unlock via the app. When I did, the GPS was functioning correctly and he was able to get the car into Drive. I picked up the MX and drove it home Sunday morning.
This is one of 3 instances that this has happened, but took the longest to resolve itself. The other two times, a reset fixed it, and the other, I was able to enable via the app, which allowed me to get the car into Drive. By the time I got home, it was working fine again. This last incident was 24 hours ago, so I would assume it's going to happen more often. My service appointment isn't until October 25th.