Then it's likely you have the very common issues, which has been discussed so many times on the forum, but doesn't have anything to do with GSX.
It's a very well known P3D installation problem that, if you upgrade P3D using the "Client" installer, the files needed to support the new menu styles won't be installed, which results in ALL 3rd PARTY addons with a menu stop working, not just GSX, but also FS Passengers, SODE, and countless of other 3rd party apps that displays an in-game menu.
The issue can be fixed by installing the P3D "Content" or the P3D "Full" installer.
