Playlists on iPad

I updated to the latest iOS app in the vain hope that it'd improve the experience of using my Naim. No such luck, the user interface is as annoying as ever. I only had a couple of small playlists on the old app so I wasn't too bothered that most of the tracks had disappeared from them. 

This evening I decided to create a new playlist to listen to over dinner. Started an album playing, then clicked on the ... and selected add to a new playlist. I then added another twenty or so albums to this same playlist. When I click on the new playlist I can see all the tracks I've added but none of them will play, I get a message that says some tracks are unavailable or offline and every track has a little cross in a red circle to the right of the track name. Meanwhile the NAS is most definitely still connected as I'm  still playing music. 

Anyone got any idea what's going on here?