So it's only recently started happening. Whenever I start playing music and minimise the app it'll close after a few seconds. Music stops, app no longer appears in taskbar or taskman. Logs indicate that windows is suspending the app but this doesn't seem to happen with any other UWP app during music playback (tried with Groove).
2017-07-14 11:40:04:9385  INFO - [WindowsAppCore] - Application is suspending (deadline: 14/07/2017 11:40:09 AM +01:00)
2017-07-14 11:40:04:9395  DEBUG - [AudioPlayerBackgroundTaskCommunicator] - Sending keys (AppStateChanged = False, MessageId = E) to background media player...
2017-07-14 11:40:05:0781  INFO - [WindowsAppCore] - Application is suspended