The problem doesn't happen if GSX is installed correctly.
- Run an update CHECK with the FSDT installer
- If that doesn't work, install the Offline installer
- If that still doesn't works, run another update CHECK again after you installed the offline installer.
- If that still doesn't work, try updating using a VPN software.
If NONE of that works, you can be sure your GSX installation is fine so, if you are still missing objects, the problem doesn't have anything to do with GSX, and it's caused by the very well known maximum Simobject limit reached in the sim, due to too high settings, especially for AI traffic and Ground AI traffic. Lower these settings and also check all suggestions in t he GSX Manual, Page 95, in the chapter named "Missing Objects"