i still use P3D V3 (3.4) ......
It's possible the bug was already present in V3.4, fixed in 4.0 and reappeared in 4.1.
As I've said, it seems related to the NUMBER of add-ons using the add-on.xml file, and it's possibly related to HOW those add-on.xml file are made. And it might even possible that the bug is there even in 4.0, but the number of addons required to trigger is not the same across all versions.
The only thing sure, it's totally unrelated to GSX.