When I set up any UA software synth in GP, when I open a saved gig file, the plug-in opens with default settings, not the settings they were saved with. These plug ins do not exhibit this behavior in Ableton or Logic, but only in GP. Just upgraded to Mac OS Sonoma, and upgraded to GP 4.8.2 (I see this was supposedly addressed from a post from February, but updating did not resolve the issue for me.) Running a 2021 M1 Macbook Pro.
Have a look at this thread: