It's their code and TV so report this bug and then decide if this is the make/break decision to keep or return the set.
My thought is that you are enhancing some copy protected content. I can't confirm but it's possible this is https://en.wikipedia.org/wiki/Cinavia
You might get around this by running the content to a receiver that will handle the sound and then the video passes through the receiver and the TV only has to deal with the video.
I Just bought a 65in Sony 65x810c 4K. I have ATT Uverse. I updated the hdmi cords that ran behind my call, about 20 feet in length. Picture and sound worked great. However when I select to Enhance to 4k through the input options. I get picture but no sound.
Any help would be appreciated