This happened to my '19 ST about 2 weeks ago. Didn't work for 2 or 3 days. Then suddenly, back to normal for the last week. My thought is that a door sensor wasn't communicating correctly (rear hatch doesn't close correctly while on an incline).
Yes, I was monitoring the Fuel Economy screen. It would state 'Engine is operating normally' (or something like that). I would try turning of the engine via button while stopped. Then it would work sometimes at the next full stop.
On a cold morning, it won't activate but the message will state 'Off due to warming humans' (or something like that!). If I turn off the Climate Control, bingo, shuts off.