This isn't a good enough answer, that it might 'possibly fix the problem'. It takes people along time to tweak their cfg to get fsx to run/look good. It should be YOU fixing this.
That's obviously wrong: there's nothing we should "fix", since there's nothing wrong with the objects, and what CAUSED the problem in the first place, is exactly some of the tweaks you applied.
Many of the tweaks found online are undocumented, which means nobody knows for *sure* if they work correctly and, if they work correctly on ALL systems and all drivers.
The only thing sure, is that with a clean FSX.CFG file, this doesn't happen so, it's clearly not a GSX problem.
Of course, this doesn't mean you can tweak your FSX.CFG, because you obviously can, but you should probably test each setting, especially the undocumented ones, and just not use what doesn't work with your system.
If you don't see problems with other scenery, that doesn't mean it's a GSX problem either, since not all scenery objects use all graphic features available with FSX more advanced materials, and these might be more sensitive to a wrong tweak, or a tweak whose side effects are not known, because not many products use FSX graphic features entirely.
