Corona 1.4
I let a render run overnight in DR mode with one additional DR machine. During the test it looked good but the final render showed a few small black areas and when inspecting the pixel values the tool displayed -nan(ind) in the original RGB values. They would've been easy to retouch in post, however after stopping the render the small areas turned into much bigger black squares which display 0/0/0 as mapped RGB values. So it ended up to be completely unusable, unfortunately I only have the state after the rendering was stopped, image is attached. When zoomed in, you can see jagged borders two sides, maybe it's useful information. Adaptivity was on, denoising too.
Is this caused by denoising? Why would a NaN pixel turn into a square?