In MSFS, GSX will ALWAYS tell a gate has a Default Jetway no matter what, because the message doesn't refer to how the jetway "looks", it refers to which system the jetway uses to work, which was really meaningful only in FSX/P3D, because there, we had TWO different systems for Jetways: Default or SODE, which worked differently, so the message was there to clarify that, so you would know how to operate them.
In MSFS, there's no SODE, so the only system available for Jetways, is the Default MSFS system, that's why the message in MSFS will always be the same, even if the jetway has a custom model.
That also explains why, if a Jetway doesn't work, it's nothing GSX can control, because the only thing GSX does, is asking the sim to make it work so, whether it works or not, is completely out of GSX control, and it's a combination of your parking position, the airplane doors setup, how the jetway has been modeled, and how it has been positioned in the scenery.
This, of course, assuming you are using GSX correctly, which includes being sure GSX Replacement Jetways are DISABLED for all 3rd party airports, because they are only meant to be used on Default airports. The manual at Page 7 clearly explains all of that, so no use repeating here but, in brief, if you don't Disable GSX Jetway replacement files for all non-default airports, you are introducing a conflict which will *surely* prevent jetways from working.
If you are sure you did all correctly, and the Jetways replacement files for that airport has been Disabled in GSX (so you will see Jetways that come with the scenery, not GSX's), then GSX is now completely unrelated to any jetway issue you might have, so it's not working, it's a problem of the combination of all above factors (position, doors, jetway)