It is happening only when I load GSX'
No, it's not. It's probably happening because you loaded SODE, which starts with the sim too.
If I select SODE 1.5.3/REload All
You have an old version of SODE. Download and install the latest one.
And, if this happens on SODE Reload All, it indicates it's a problem with SODE or, most likely, a 3rd party scenery that uses SODE jetways you haven't installed properly, or haven't uninstalled properly.
GSX doesn't have anything to do with this, and those jetways are coming from a 3rd party scenery that used SODE, so they are entirely handled by SODE.