Since changing the temporal history buffer to 11:11:10 from FP16, it looks as there is visible dithered quantization to remove banding when rendering. (Taken from conversation on Forum Post linked from Nick P.)
[Image Removed]
RESULTS: Note where the HERE label is pointing in both areas, there is a dithering pixelated look in 4.9.2
EXPECTED: The Smoother look of 4.8.2
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-21858 in the post.