DJM A9 keeps cutting sound with Rekordbox

When connecting DJM-A9 with Rekordbox (windows) as an external mixer or through Pro DJ Link with CDJS and mixer, The output sound keeps cutting off, although the track is playing and you can see it on the computer screen (or the CDJ) 
The channel faders vanish with the sound, then kick back in after a couple of seconds.
Tested this on 2 different DJM-A9s and the same problem occurred. Any solution?? perhaps new mixer firmware??