Since the problem doesn't happen here, it can only be something specific to the scenery you use so, as we always asked when reporting any problems, always include ALL the following informations:
- The airport used. If the scenery is not default, clearly identify it.
- The gate used
- The airplane used. If the airplane is not default, clearly identify it. If possible, indicate if you used a custom configuration file for it.
- The exact sequence of GSX operations.
Of course, before doing any of that, be sure you use the current version of the program.
If you missed a Minor Update in the past, you can get it by simply reinstalling GSX with the installer you have.
If you missed a Major Update in the past, you'll have to download and install the latest Stand-Alone Addon Manager