Apple TV 4K + LG OLED55C7P + Playbar/etc. + Belkin Ultra High Speed HDMI Cables

So I recently invested in the LG OLED55C7P, which is gorgeous. I can now run my individual HDMI sources (Cable, Apple TV 4K, Xbox One 😵 to the TV, and audio out through optical to the playbar and beyond. All was good for video and sound - 5.1 for each source, and I didn't need a splitter (I used the Octava before, with my old TV).

In reading about Dolby Vision, etc., I saw that Apple recommended the Belkin Ultra High Speed HDMI cable. I saw conflicting opinions, but I wanted to use the best that I could, so I bought the cable and stuck it between the Apple TV and the TV. Boom - I started getting the 'Unsupported Audio' error in Sonos. I recycled power for everything, tweaked the TV audio output settings, tweaked the Apple TV audio output settings, and no luck. So, I swapped the good old HDMI cable back in, and life is fine.

So my question is - does anyone have perspective on why this cable, which I'd assume would be backward compatible, would have issues? The TV (2017 model) can pass through Dolby Digital/DTS multichannel via Optical, and it works fine with the non-Belkin cable between the Apple TV and it. I'm still getting Dolby Vision via the Apple TV with the old cable, so I don't seem to have lost anything, but it didn't make sense to me, so I figured I'd ask the experts!

Thanks in advance for any thoughts.