in several airports asking, after the arrival, for the parking gate, only few of them are showed (one example is Aerosoft LIBD where only the parkings and not the gates are showed).
It's not very clear from your message if you are missing the *actual* gate objects, or you are missing some parkings from the GSX parking selection menu.
If you are missing the scenery objects, that doesn't obviously have anything to do with GSX, which is entirely unrelated to how the scenery will look like.
If, instead, you are missing parkings from the GSX parking selection menu, the first thing to check, is to be sure GSX is using the correct AFCAD for the scenery, instead of another one in conflict. You can check this with the "GSX - customize airport positions" menu option of the Couatl menu. The window that will open will indicate the name of the AFCAD in use by GSX.