Or maybe restore the default ones that were deliverd with the scenery and let GSX use the default ones?
That's what you are always supposed to do when using a 3rd party airport! GSX is not supposed to replace jetways at 3rd party airports, the set of replacement files in GSX is only valid for default airports, that's why there's a "Exclude 3rd party" button in the GSX Config panel, which you should use each time you add a new scenery.