I’d try deleting the local file, then re-download it from Apple. It may have DRM on it, which Sonos can’t interpret (but Apple Music can). A ‘newer’ version of the file may not have DRM on it. 

So I deinstalled the album (didn’t delete it) then downloaded it again. No change. Then deleted it. Reinstalled but the tracks just won’t play using the Sonos app. Downloaded a different album of theirs with many of the same tracks which must be Sonos compatible. All good. Thanks.

Jane

Odd. I’d still guess some DRM remaining on those tracks, but I don’t have access to all the data, so who knows. It will remain a theory.