I'm on P3D v3
Doesn't make any difference, it's exactly the same as FSX regarding this matter.
[I tried my best to help you narrow down the problem as I'm a commercial software developer, too. None of the fixes helped, the only way to avoid the problem is by not using any GSX service at all (also no pushback). The only thing I can do now is to offer my system as a test bed to find the problem.
There's nothing to test. The 32 bit version of the software wasn't affected by this bug so, again, your problem it's just that, adding GSX L2 to your already overstuffed installation, has reached the limit of what a 32 bit simulator can do.
As I've said, you still have the option to restore default jetways, of course. Passengers will still be there on open parkings, and if you customize a single 3rd airport, it shouldn't affect your flying elsewhere.
You can try using the 1K/2K replacement jetway textures too so, it's not is that you don't have options.