You must have updated the simulator, and haven't noticed the message which said that, due to an update of the simulator, you must disable the default jetways on default airports, with the GSX Control Panel.
Default jetways are disabled automatically when you install GSX but, any simulator update or reinstall, they'll be back so, in order to save you to have to reinstall GSX again each time you update the sim, the GSX Control Panel has buttons to Disable/Enable default jetways.