I already made this setting. I am now trying the “Plex dance”.
Marmite
EDIT: Currently, after 2 hours of the Plex dance (with content removed, trash emptied, content replaced, and Update Libraries, Scan Files, Refresh Metadata), Plex web player recognises that there are 9371 items (correct), 1093 albums (there should be 1055), and it has not recognised one genre, nor displayed one album art image. Gonna leave it overnight to have a good rummage in the files.
