This has been discussed several times on the forum and, of course, it's not a GSX error, it's an intentional change, due to a change in the simulator itself.
After some update ( SU10 or 11, not sure ), the simulator *itself* has changed its behavior and, if a gate has a jetway, it will automatically operate the main door on its own. This conflicted with GSX own automatic operation of it, resulting in a double trigger (closing+opening in succession)
So, to FIX this problem due to the simulator change, we updated GSX to not operate the main door automatically anymore, so it's all normal.