I agree buy the APPLE RECOMMENDED LEAD! I really cannot understand why people aren't buying the RECOMMENDED HDMI lead from Apple. It's been designed from day one to work with the ATV 4K. It's crazy that people spend £2000++++++++ on a TV and set up and complain about a 30 dollar lead which is only bought once! I just don't understand. Surely, if Apple recommends ONE particular lead to work with the ATV 4k 100% of the time, then you simply buy it at the time of buying the ATV?????????? I've always bought the Apple recommended HDMI leads from the ATV 2, 3, 4 to 4K and i've never had an issue. Ever.
It's as though some people think that they know more than the actual people at Apple who are designing and implementing this tech.
The fact that a lead is not certified does not automatically imply that it cannot function properly (hence the term "recommended"). At any rate, I can get hours of perfect Dolby Vision picture, with my issue only arising during protracted periods of standby (during which, presumably, only CEC-related signals travel through).
By the way, the impact certified lead has can at times be negated by a multitude of factors, including the quality of a TV's internal wiring. A chain is only as strong as its weakest link, and cables are by no means a silver bullet.
Cables are only one part of the equation, and I am 100% confident that they have no bearing in my case.