Hi, I was one of those who tried using the new link, uninstall and reinstall without success, and for a while only had the MSFS version working.... BUT... now both my GSX are working in P3dv5 and MSFS. Just wanna share here what I did differently. Hopefully it will be of help to anyone who is still stuck.
1 - Open "Addon Manager" folder in C:\Program Files (x86)\Addon Manager(or wherever you installed)
2 - Look for "Couatl_Updater" and "Couatl_Updater2" application icon.
3 - Right click on each files above, select Properties, go to Compatibility tab, Check "Run this program as an administrator"
4 - Now right clcik on "Addon Manager" folder, select Properties, under Security Tab, Click edit, check the "Full control" and "Modify" box.
5 - Right click FSDT Installer icon at Desktop, select "Run as administrator"
6 - Once the program loaded, press "Update All"
7 - Restart PC.
8 - Run MSFS, Load your flight, then right click "Start Couatl for GSX MSFS" icon (at Desktop) select "Run as administrator"
9 - Press the GSX button in the ingame menu, wait for the airport cache to complete. GSX menu will appear when all is completed.
For P3dv5 no further steps after step 7.
Hope this helps.