Very frequently I receive messages that the music on my playlists is unavailable. Also, when I click on “Artists” I only see 2or 3 dozen artists listed despite that when I search for a specific artist their albums appear. When I hard boot my server (innuos zen mk3) the problem is corrected but returns when I shut down and activate Roon Arc.
This seems to a common issue at the moment, unfortunately, see the various complaints here:
For your specific case, it would be best if you open a new topic in Support (instead of Uncategorized where you posted now) and fill out the question template with all the details about your setup.