Sorry, yet-another broken album art post... I've read through a bunch of them and unfortunately I don't see exactly the same issue.
Setup background: Plex is running on an NVIDIA Shield TV Pro, with the media library on an external HDD plugged in via USB. Most albums have album art embbedded in their ID3 tags, and all albums have a folder.jpg file in the same folder as the mp3's.
TV and Movies are working fine, and I had my music loaded pretty well, too; there were some of the expected "Plex shows artist image instead of album image" issues but hitting "refresh metadata" usually fixed it all. Then I moved my library to another HD. Plex had trouble handling the new locations, so I deleted my Music library from Plex, cleaned bundles, emptied the trash, restarted the server, and created a new library pointing at the new location.
Now, none of my albums or artists show any art, and "Refresh Metadata" does nothing. I've done the plex dance with every media agent order variation I can think of, but the results are the same; the bulk-refresh I used to fix things the first time around just doesn't work.
The only way I can get album artwork to show up is by hitting "edit" on an album, going to Poster, and selecting the cover image there. But I have 3300 albums, and doing that one by one is... unappealing.
Is there a way to force Plex to auto-select the first available image in the Poster tab? Or, barring that, is there some other combination of steps I can take to force a refresh? I'm really regretting nuking my library in the first place :(