atom mute with spotify connect (sometimes)

My Atom is connected wired to my router and I'm using an iphone connected wirless to the same router, on the iphone I've installed the naim app and spotify. Now I'm testing spotify connect to the atom.
It works well most of the time but sometimes, when I manually change song on spotify, tha atom remains mute: I see the new song cover on the display, I see the song time going on on the phone but not on the atom, it remains mute and the time do not progress.  To make it work I must slide a little bit the time bar on the naim app, and tha atom starts to play the song.