Album art not showing

I have Roon Core installed on my Innous Zen Mini III and use the control app on an Android Tablet. I mainly stream from Qobuz and have a handful of albums downloaded to the Zen Mini to plug gaps in the Qobuz catalogue.

I noticed the control app was taking 9gb of memory on my tablet so I cleared the cache. This reduced memory usage to 6gb but many albums now don’t show artwork.

Music continues to play with no problem.

Any suggestions?