I have used this soundbar since Dec 2015 and when playing Blu-ray or DVD discs, the sound drops out intermittently, for a few seconds.  I have noticed that this problem appears on other Sony Soundbars. 

Connections, Optical Audio out cable

Blu-ray Sony BDPS1500 HDMI Gold cable

TV Bravia 32CX523 HDMI

At the moment I have changed the optical cable from the one supplied by Sony, to a thicker one purchased online.  I will update this post if that has solved the problem.