That would be correct behaviour for a stereo sound stream form your TV. Is that when this happens?

yes   just been watching a music documentary and when the  talking was on this happened but when it cut to the music, in between the talking, the 100s worked fine

That does sound like you’re expecting something surround sound isn’t. Dialogue should come from the soundbar, not from the surrounds like you seem to expect.

What does the app say you are getting as a sound format?

Beginning to make sense. Thank you. It says Stereo PCM

BTW the TV input comes from an IPTV box 

Is the box connected to your tv? You could check the audio settings of the box and your tv. Both have to be set to Dolby Digital 5.1 or bitstream. 
If your TV doesn’t Support multichannel audio passthrough from hdmi sources, a hdmi audioextractor could help. 

Yes it is  and thanks. I will check. Very much appreciate your help. Alan.