Some models pause selected functions when the door opens. That can be intended behaviour rather than evidence of an intermittent motor.
What the observation means
The response differs by mode and appliance; a cooling fan and a cooking fan may also behave differently. Opening the door repeatedly to watch the fan changes the programme and increases exposure to hot air.
A useful next step
Check the manual's description and report whether the problem occurs with the door normally closed. Do not press or tape a door switch to keep the fan running while open. A new scraping sound, smoke or failure during normal closed-door operation still requires assessment.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.