I was unaware of this responsibility as I don't see anything about it in the manual.
That's because it's not a GSX-specific issue, but something you are supposed to known about the latest MSFS version, and whether the reordering works or not, depends on the simulator.
I was able to move GSX jetways up a couple of sections but then it got stuck and now it won't move anywhere
By moving them up, you made the thing worse. Loading order in MSFS works the opposite way than FSX/P3D, the items DOWN are loading after the ones UP, meaning they get an higher priority.
In your video, you have many packages and you are scrolling them so fast, that I can't be sure of the ordering.