Unfortunately, one of Plex’s major failings is albums with multiple artists. That is at least part of the problem here. There’s a feature request (yes, it’s several years old). You may want to add your vote.
You might try doing the Plex Dance on one of the albums that is being mis-attributed to see if it corrects itself (the Plex Dance is a workaround for a serious problem that was so pervasive that it was given a name. They’ve eliminated the need for it in nearly all situations for music, but it’s still necessary in a couple of instances).
note: The Plex Dance involves removing the album from Plex and re-adding it. If the album or any tracks are included in playlists or collections, they will be removed from them.
