My car did this today as well. I think it's related to turning on the climate control before entering the car. Today I turned on the heat before I put my kids in. I took them to school and went home. When I got out and closed the door I noticed the car was making more "noise" than usual, so I opened the app to see if anything was happening. The app opened directly to the climate screen and showed that the heat was still on full. I turned it off with the app and all was good.
I have pre-heated/cooled the car before and it did not stay on after driving, so I'm not sure if this was a fluke or if something is wrong. This is the first time I've pre-conditioned the car with my new phone though, so that may be a clue (previous iPhone X, current iPhone 12 Pro).