I’m assuming you’re using a stock or a good device handler for your garage door controller and that no SmartApps or Automations are interfering with your Garage door.
You can check you device events logs in the IDE to see if SmartThings sent a command to the garage door opener. IDE -> My Devices -> < garage door controller > -> List Events
If there’s nothing in the events then the garage door controller itself may be facing an obstruction while opening and closing itself. It’s happening after a it completely opens and stabilizes, then it’s likely some automation you may have that’s sending the command (are you using any virtual garage doors setup which may be triggering it?)