There is no interaction between GSX and UT2 if you are running either FSX or FSX-SE.
There isn't supposed to be ANY interaction between GSX and ANY AI Traffic product. GSX relates only to your own airplane, and it doesn't have any relationship with AI.
The only thing GSX does related to AI, is to ask Simconnect where they are, in order to tell you if a parking is taken.
I still don't know why but UT2 traffic stops working, and I have to force it to "Increase the Traffic Density" to spawn AI aircraft while at any airport that is not Virtuali. It doesn't work at all at any Virtuali airports only works on generic and Aerosoft airports.
I cannot see how this could have any relationship with any of our products. You said yourself you have issues at non-FSDT airports too, and we surely don't have any control over AI traffic outside our own airports.
Do you guys at Virtuali have a fix for this?
Not sure why we should have a fix for UT2. One of our developers uses the latest UT Live, and he never reported a problem with it, just that, being a beta, it sometimes have issues on its own.