Door gasket
Check your door gasket to be sure you are getting a good seal. My stove did the exact same thing, turns out the gasket wasn't making contact all the way around. I had just replaced the gasket in mine but new doesn't always mean better. Since my stove has glass in the door, I decided to pull it out and look inside to visually inspect the gasket while the door was latched and that was when I found the problem. There were a couple of places where the gasket wasn't quite making contact. I replaced the glass gasket, installed extra door gasket cement in the places where it wouldn't seal, and reassembled following instructions for the cement. I haven't had any more problems for over a month now.
To check your door gasket another way, use a piece of paper (similar to a dollar bill) and check how much "drag" is put on it when it is pulled through the sealing area. Be sure to check all the way around the door since it could just be 1 small area not sealing.
I still do not know why mine didn't seal completely all the way around with the first new gasket. Maybe the door is a litte warped. Lesson learned, always check your work after you have finished. BTW, that door gasket cement is not fun to remove after it dries, I did most of it with a hand held grinder and wire wheel. Make sure you have proper PPE on since those wires fly in all directions.