I’ve just tried that still no change and it’s not a 4K it’s just the smart tv not sure if it’s to do with any of the Xbox one settings either
I don't own an Xbox, but have you tried this :-
On your Xbox, go to Settings, then Volume and audio output and Speaker audio and try the different HDMI settings (start with Stereo).
Also have a play around with the sound settings on your JVC television.
I would also be tempted to try a different HDMI cable and HDMI port on your television.
Also do you own another television in your home to temporary test the Xbox One NowTV App on to see if the same symptoms persists with no sound ?
Thanks for your help I now have it working!