First, it's always best to make precise, exact, report of the situation you are in.
- If you are in a 3rd party airport, and you haven't excluded it from jetway replacement, Jetways will *invariably* fail, because the Jetway replacement files for GSX are only meant to be used with default airports.
- If you are using a default airport, jetways in GSX have the same, exact position and dimensions of the default ones, and there's no other way to do it and be sure they would work as a stand-in replacement. This means, if they were badly placed in the default airport, they will be just as badly placed with GSX, they will just look better.
Also, GSX jetways are 100% standard, which means they have exactly the same issues as any jetway from any developer, including the default ones so, they dock in strange places, like the passenger back door and sometimes they even dock on the service door with the head turned!
Sometimes the dock at the right door, but the don't fully extend, because you are parked too far.
This is completely out of our control, the simulator decides how and where to dock a jetway, and there's no way for GSX to even *know* where actually is so, when can only hope that, through parking customization and the use of the TEST function of the parking editor ( Press NumPad5 while you are editing a Parking and see where the jetway goes ), users will be lead to park in a sensible position resulting the jetway docking correctly on the correct door. When this is achieved, everything works.