If the supplied jetways don't work properly with PMDG 777, I would have to delete the relevant *.bgl files from the scenery and then replace them with GSX jetways, very complicated and a lot of work...
As I've said, there's no telling what you can do, without knowing if you are using SODE jetways or not, which as I read on the Aerosoft site, are an option on the scenery. That's why I said to check the GSX customization menu, which will tell you exactly which jetways this scenery is using.
If they are SODE jetways, they are not in any .BGL, but the XML SODE folder under C:\ProgramData\12bpilot
If they are standard jetways, they are in a .BGL, and can be excluded either by removing their .BGL library file, or following the GSX suggested exclusion method, which is explained in the manual, and we have a video tutorial linked as sticky on this forum.
In any case, regardless if the jetways are standard, or 3rd party SODE, GSX has no control over of well ( or how bad ) they work.
But that's one of the points of GSX L2: you can replace jetways from a 3rd party scenery, and you'll find the GSX ones usually work better, if only because there's plenty of models of different sizes, which makes impossible not being able to find a jetway that doesn't solve on a particular gate.