I was having the same problem after upgrading from P3D 4.3 to 4.4. I didn't use the scenery in 4.3 version so I am not sure if it started to happen after upgrading to 4.3 from 4.2.
I used Virtuali's tip but only applied it to KLAX scenery. Didn't re-install GSX 2 Expansion.
Seems to be working for me.