Hi Russell
I once saw something similar when I was viewing a Flat in The Sky X Pro Camera Control Module and I had the Histogram set to a funky stretch from playing around with a recent image.
When I re-set the default Histogram stretch, the flat appeared normal as per my other Flats.
It seems that my funky manual settings somehow crushed some of the displayed data, leading to speckles quite similar to yours. The actual data in the file was okay.
Hope its as simple as that.
Cheers
Dennis