If after an update, you missing artworks or other metadata, and Plex refuses to add them when you press “Fix Incorrect Match”, here are the steps to follow:
cd "/var/lib/plexmediaserver/Library/Application Support/Plex Media Server/Metadata/TV Shows"
rm -rf *
cd "/var/lib/plexmediaserver/Library/Application Support/Plex Media Server/Metadata/Movies"
rm -rf *
Then, press “Fix Incorrect Match” again, and metadata will be back 