Missing artists in search

Sorry if this is already covered elsewhere but I can't find it in any forum search.

I'm not a geek and have an old school view of technology so bear with me....

I have:
Sonos kit in lounge & kitchen
Multiple devices with Sonos controller app
iTunes library recently moved to a NAS

A problem:
When I search for an artist on Sonos app, tracks that are in the library don't show up on artist search when they are part of a compilation. In iTunes library they are correctly configured eg Album = Saturday Night Fever, Artist = KC Sunshine Band, Track = Give It Up. In Sonos it comes up with no matches for search in Artist = KC Sunshine Band

In Sonos, when you click "Artists" in the Library, the first entry says (Compilations) and that's where the relevant album/track actually resides.

Help ?