Over the last few weeks I have noticed that album and artist images have been disappearing. When going to check and edit the missing object it turns out that image is still there it’s just been unselected (image below) Its the same for everything that is missing. A metadata refresh doesn’t make any difference. Any ideas of a fix will be helpful, otherwise I will have to go through all artists and update manually.
Are you employing an anti virus software on the server computer (or your router)?
Some of these are blocking access to archive.org, where some of the cover pictures are hosted.
After you Refresh Metadata of the album or the Artist, you should see notification about the blocked access in the activity logs of that anti virus software.