When they are greyed out, Sonos cannot find them. Are the flies on your computer?

Maybe they are protected by Apple DRM?
 

Are the albums/tracks ones that you can access via other third party devices?
 

If accessing them via previously saved playlists/shortcuts, perhaps the versions are no longer available or have been moved, in which case try searching for them again and if found and will play, then replace the track in your playlist with the one that plays.

Yes