I have noticed a related issue when using JRiver Mediacenter (DLNA playback to the SA30). Changing the playing position then also doesn’t work, but the music then skips to the start of the next track.
This is exactly the behaviour I’m experiencing with Arcam Music Life iOS app, build 3007. Therefore I think the issue you’re experiencing has the same cause. The latest status from Arcam is: they are trying to reproduce it, they are unable to reproduce it. I’ll attach your information to the ticket.