I got my XR a little over two weeks ago. I spent the first day in my office at my stand-up desk on my Onewheel just getting used to rolling around on it and practicing dismounts by lifting my heal. Every once in awhile, the motor didn't disengage when I lifted my heel. Then I would lift my heel and drop it a few times to get it to stop or pivot my toe towards the front of the board to get off of the toe side sensor. Twice the board took off across my office after I hopped off but I thought it might have my inexperience.
I was going to call FM after the first three days I had my OW which was a Friday. I decided to ride it through the weekend to see how it would do. The next day I showed it to my trainer who has had one for about two months. She rode it and noticed it wasn't disengaging. Then she had to hop off and it took off, running into her partner who kicked and it did a u-turn, went another 10 feet and hit a 70 year old woman in the shins. Not good!
I didn't ride it anymore and called FM on Monday. They sent me mailing label for the footpad. I checked with them a few days later and they said the techs couldn't recreate the issue. Luckily, I had taken a quick video in my office where I clearly lifted my heal several times and the motor didn't disengage. It only did stop when I swung my toe to the front. They saw the video and immediately sent me a new footpad. It is operating nicely now.
You have a bad sensor and you need to get it replaced. You don't want your board flying out into traffic or pedestrians. Good Luck!