For the album to stay “together”, it is also necessary that each and every track has an identical ‘Album Artist’ meta tag.
This is particularly necessary if some tracks have a different ‘Track Artist’ set (for instance if there is a guest artist on that track).
An album “split” can also happen if some of the tracks have a ‘track number’ and/or a ‘disc number’ set in their meta tags and some tracks don’t have these tags.
Don’t forget the Plex Dance after editing metatags or renaming media files.