AlbumArtist misses artists

[Peter26J]

I'm playing with minimserver for two weeks now and today I found that at least one artist is missing in the AlbumArtist list. I saw this on BubblePNP and tested it on VLC as well and see the same error. I can find the artist in the list of artists, but they are also in the AlbumArtist field.

The artiste is "La Petite Bande" and is used in the AlbumArtist field together with the conductor "Sigiswald Kuijken" who is also not listed in the AlbumArtist field.
To be clear, the tracks of this album have two AlbumArtist fields.

When I search the same albums under Composer Bach, and choose AlbumArtist these albums also show up, but under a section '[unknown]'.
Under section '[unknown]' are more albums that definitively have an AlbumArtist and are not unkown.

I tried rescan and restarting minimserver, a few times, but to no avail.
I also deleted the profile with all my settings and importing it again, but that also does not work.

See also my attached screenshots.

I'm running MinimServer 2.2 update 238 on a Synology DS920+ that is fully updated.

Any ideas what to do?
Thanks for any help.