How does the lumin software read the files? It seems like it does not completely read how it's tagged.
When you use a NAS, Lumin players do not read the metadata of the files directly. The UPnP server running on your NAS read those metadata from the music files, then create a XML description of the file to be obtained by the app and the player.
If you still experience those issues after using MinimServer, then the tags of the music files need to be examined.