It's possible what you are seeing is not the jetway disconnecting, but a known visual bug of the jetway losing sync between its LODs, showing different LODs as if they were disconnected, as explained here:
https://www.fsdreamteam.com/forum/index.php/topic,27550.msg180461.html#msg180461You can verify if this is your case, if you go in the external Showcase drone camera, and move it around a bit, getting closer or far away from the jetway. If you see the jetway "snapping" into the connect/disconnect position while the camera goes away or get close, the problem is in fact the one already discussed above, so it's completely unrelated to GSX, and always happened with default jetways on default airport even without GSX installed or even before it came out.
If, instead, this is not what you are seeing, it's possible you are using an airplane than can control the jetway itself ( Fenix ? ), in that case you must disable the jetway auto-docking feature in the airplane.
