It usually helps to uninstall the Groove Agent 4 content and then reinstalling it. Also, make sure that GA4 is updated.
There’s something about some Windows installs that’s causing some of the stock libraries and expansions to not be detected on the first try by GA4. Groove Agent 5 is probably going to have an enhanced library system similar to Halion Sonic 3 and Halion 6, which hopefully will make these issues go away forever.