Now we are talking, with default AI it connects without any problems
Well, at least you should now be convinced the problem ARE THE AI, not GSX.
So where is the difference to FLAI models?
It might be a difference, even a small one, between the SODE internal models database ( which SODE uses when its on its own ), and the data GSX gets from Simconnect.
SODE has a database of generic models, while GSX uses its own data, which is usually way more precise, because it's made for the user airplane, so users can customize very precisely their own airplane for GSX, and this will sent to SODE, which will use it INSTEAD of its own generic database when it's used together with GSX.
While this is clearly better for the user airplane, when AI are used, GSX is not using its own database ( because it refers to specific user airplanes so, a PMDG 737 is NOT the same as an iFly 737 ), it takes data from Simconnect, which means it takes you [Exits], and applies a generic correction, because the data on the [Exits] refers to the CENTER of the door, while the data GSX and SODE normally use are referred to the BASE of the door, which of course is the better approach for service vehicles, while the center might be more useful for jetways, which were the thing the [Exit] data was initially designed for.
SODE has its own database of generic models, and it also applies an offset, and has some correction factors is, which means what you put in the [Exits] section is not used "AS IT IS", neither GSX or SODE will use it as it is, each one will have some correction applied, and your problem might be you are off of JUST enough to make one correction working, but not the other.
I'm sure you should be able to find a value for the [Exits] that works both for GSX and SODE.