Accessing iTunes servers displays albums multiple times

I have a number of albums with multiple artists involved. Some I’ve imported from CDs, some bought on the iTunes store. In iTunes these albums display correctly as one albums containing all the tracks. But I have two scenarios involving other apps accessing iTunes albums that don’t work.

The first is where I use VOX to read the iTunes library, the second is where I use iTunes to access an iTunes server running on my NAS.

In both of these scenarios, the album is displayed multiple times, broken up by the track artists instead of the album artist.

For example, the Adjustment Bureau, albums artist: Thomas Newman. Contains a couple of tracks done by Richard Ashcroft and Sarah Vaughan. This was bought from the store so should have the correct metadata.

In iTunes: Displays correct as one albums.
In VOX accessing iTunes: Displays as 3 albums, one per track artist.
In iTunes accessing NAS iTunes server (Synology): Displays as 3 albums, one per track artist.

If I had to guess I’d say the problem is that the format of the file that iTunes makes available has changed. But I don’t know how to fix this.

Has anyone had the same experience? Fixed it?