You don't say which airplane you use.
With the Fenix A320, you must disable the feature to connect the jetway automatically, otherwise GSX will connect the jetway and the airplane will do that as well and, since the standard connect command is NOT a "connect" or a "disconnect" command but a "toggle" ( invert the status ), the two doing the same thing will result in the jetways disconnecting.
If, instead, you are using an airplane that doesn't operate the jetway, it's likely you are running into a different problem entirely, which is the loss of sync between the jetway animation and its LOD levels, which of course is not a GSX problem, but an MSFS bug that affects each and every jetway in the sim, including the default Asobo modes, see here:
https://www.fsdreamteam.com/forum/index.php/topic,26965.msg176552.html#msg176552