I got two certified HDMI cables at Walmart (and cross referenced the certification online). One of them worked fine, while the other one worked in a basic sense but failed to negotiate and wouldn't give me all the fancy sound and video options going from my Shield to my LG TV. The other cable, nominally identical, worked fine swapping between them so the other one must have been bad and I ended up returning it for another one that worked.
So even the certified cables can be defective it seems, and more confusing is that they still mostly work. The defective cable would still negotiate 4K and show a nice image, but wouldn't work with stuff like Dolby Vision (and a couple other more advanced modes but that is the one I remember). I probably would have just assumed something else was wrong with my setup and written it off if I hadn't bought an identical cable to swap. I bet a lot of people wouldn't even notice the missing functionality, which is likely how this has become so widespread.
So even the certified cables can be defective it seems, and more confusing is that they still mostly work. The defective cable would still negotiate 4K and show a nice image, but wouldn't work with stuff like Dolby Vision (and a couple other more advanced modes but that is the one I remember). I probably would have just assumed something else was wrong with my setup and written it off if I hadn't bought an identical cable to swap. I bet a lot of people wouldn't even notice the missing functionality, which is likely how this has become so widespread.