The reason I thought GSX had something to do with FSX ATC is that GSX unloading servies at a gate for heavies at KATL upon arrival was turned down.
GSX doesn't have (and never had) any interaction with the FSX default ATC. Nothing you do in the ATC or in GSX will affect one or the other.
Also at KSAN, the FSX taxi (yellow arrow line) would not show up when I selected it. These things never happened before the GSX update at these airports which I use frequently.
This doesn't have anything to do with GSX.
At our airports, due to the way the ground is made, is to be expected not having the progressive line, but that's an issue of the SCENERY (and there's nothing we can or would do to fix it, because it would require going back to the slow FS2002 ground polygons), not of GSX.
If you don't see the progressive taxi on a 3rd party scenery, that's just because they might have used similar methods in the scenery too.
Again, nothing that has anything to do with GSX. Fact you only noticed it after the GSX update, it's just coincidental, but it would have been exactly the same, even if you didn't update GSX.