In the GSX internal configuration, the airplane is configured to have the main passenger Exit, located on L2 so, passenger will surely use that, because there are no other exits. However, if you have a custom airplane profile, it will take precedence over the GSX internal configuration, and if it's configured with other exits, it will cause a problem in this case.
Check the airplane configuration page and, if it doesn't say "GSX Internal Database", press the RESET button to restore it to the configuration that comes with GSX.