Naim App issue - track in Play Queue but plays silently...

Has anyone else experienced the following issue?

Very frequently (it's possible that it's every other time, which may or may not be significant) I select a track or album to play (using any of the possible selection methods) but I get silence, even though the Play Queue shows that the track has been selected and the time elapsed line and counter are moving along...

To correct it, I have to clear the Play Queue and start again, which (I think always, but it might be almost always) fixes the problem...

Does anyone have any idea how to fix this? It's most infuriating...

I've (only just) emailed Naim Service so when they get back to me I will post their views, but in the meantime if anyone out there has some ideas I would, as ever, appreciate it...

iPhone with iOS 8.1.2

Naim App 4.3 build 10088

ND5 XS with firmware 4.1

Nick