Jetway replacement in GSX are supposed to be used with default airports, because they only work if the parking numbers and positions match the scenery.
When you use an add-on that comes with its own jetways, is best if you Disable the GSX replacement file, which can be done from the Config button in the FSDT Installer, with the "Exclude 3rd party" button, which will automatically search all add-on sceneries and will move to the Disabled list.
