We did not spot this flaw in the 21AXP22 phosper screen until today. It appears to be a break down of the material between the pixels. The first two photos are with the Sony A6300. The third is by the Apple iPad Pro 2, 10.5. It looks like a total of five pixels are contaminated. The Apple barely resolves it.
The lens on my Sony is a medium class lens. Since it’s an interchangeable lens camera, a good macro lens would resolve the pixels razor sharp. Still the lens I have, did a nice job in resolving the pixels at 3 feet.