Well, I’ve the same problem;
Some of Steinberg loops do not appear under Loops & Samples at Mediabay Right Zone.
For example I install “Loopset Ambient Lounge”. I can find it under Mediabay (F5) and load samples. But cannot find it at right zone!
Also some of Groove Agent libraries are seen at the right zone, some are not. The ones that are not seen at right zone can be found in Groove Agent. So the problem is with mediabay right zone.
I have removed not seen libraries from Steniberg Library Manager. I downloaded them again via Steinberg Downloader. I installed them to the default install location. But I still can’t see them at right zone.
I upgraded my Cubase to 11 at studio, it can show all installed products at medibay right zone with thumbnails. But my Cubase at home studio has this problem.
Then I found something about this!
There is a section called “Content Set” in media bay window. If this part is empty then the VST does not seen in Media Bay right zone. If is named such as “Trip” then you can see it under Halion Sonic at the right zone. Check the attached “S1” picture. For example as you can see at the screenshot, I can find Marco Minnermann Kit when clik on Groove Agent in Media Bay Right Zone, but cannot find Funk Essentials which its content set part is empty. But I cannot edit or rename this Content Set part.