Music not playing

I've linked the Alexa skill and indexed the music on my DLNA sever. Generating the library report shows that all the music is there and if (eg) I say "Alexa, ask our jukebox to play Waterloo by Abba" then Alexa tells me it's playing but nothing actually plays. If I immediately try "Alexa, ask our jukebox what track is playing" I get told that Waterloo is playing but it still isn't playing.

Any ideas for what to check/how to troubleshoot?

Steve