I see that my skins are stored in AppData-Roaming-JAlbum-Skins.
I presume this is normal and shouldn't get touched with a Windows Update?
That's correct.
I think the Jupiter skin(s) somehow reverted to default settings as you say.
The skins, when you download them from the jAlbum site, are stored in that
AppData location. But they're never changed by anything
you do. When you use the skin to make an album project, your changes from the defaults aren't stored with the skin - they're stored with the
project, in the
jalbum-settings.jap file. That's the file that gets saved when you tell jAlbum to save the project. Your projects are stored wherever you've told jAlbum to store them - by default,
Documents\My Albums.
None of this would be affected by an operating system update. Please trust me on this - I've been through countless Windows and macOS updates over the last 15+ years, and none of them has ever changed
anything in my jAlbum installations, in my skins, or in my album projects.