Thanks for the quick response!
I have change to software mixer and the issue and log file is exactly the same.
Regarding
2017-05-15 12:25:30,328 WARNING [26095:MainThread] mopidy.audio.gst: GStreamer warning: gst-stream-error-quark: No volume control found (3)
…another post suggests this is no prob.
So the question is: Where is the problem then?