This one is nothing. There's a really bad one that's been around several years, to this day unacknowledged by Adobe, even after several long discussions in the Adobe PS forum.
Typically, this bug shows up in ProPhoto files, as distinct cyan banding in the shadows, when you have GPU set to "Normal" or "Advanced" modes. In these modes, the display color management logic is performed in the GPU. When you turn it off or set it to "Basic", these color transforms are shifted back to the CPU - and the banding disappears.
And the really interesting part is that even sRGB as display profile exhibits this banding. So there's no doubt it's a real bug, and not faulty calibration or bad profiles.
But it doesn't stop there - even Adobe RGB and sRGB files are affected, although not as severely. There's no banding here, but black levels tend to get clipped a couple of values. This seems to affect LUT display profiles more than matrix.
But in all cases, relieving the GPU of color management and shifting it back to the CPU removes the problem altogether. Poof - gone.
And for all this - has anyone ever seen any speed improvements in Photoshop? Not me. So I've kept it at the "Basic" setting ever since. But I could probably just turn it off altogether and be just as happy.