As suggested by someone who had the issue with P3DV4, I reinstalled GSX and all is well.
Yes, all our sceneries that use SODE jetways require GSX to work.
Strange though as my Addon Manager had indicated GSX was installed
The Addon Manager won't tell you if GSX is installed (only sceneries are detected for being installed "in the scenery library") or not, it will only tell you if it's active or in trial, but this is unrelated to the installation of the product on the system, since you can uninstall/reinstall an unlimited number of times without any effect on the activation.
I had ran the FSDT Live Update several times.
This is normal: the Live Update will update only files for products that are installed so, if GSX wasn't installed at that time, the Live Update won't bring it up.
We'll try to make more clear diagnostic messages from sceneries that requires GSX to work with the next updates.