This is very hunchy, but I believe I've seen effects such as this when exporting "extremely" processed files at certain pixel-widths. The result is, in effect, a rectilinear moire, and the solution iirc was to choose an export width that was a multiple of some of the common denominators of the original image; eg for a 2400 pixel width, I might go with 1200, or 1600, 800, or 600. After writing above, I took a look at your two images in LR. Saw the output was tilted, experimented to see that tilting the original 1.19 seems to be a perfect match, and also matches your output's dimensions. Rules out my first theory, now I wonder if the tilt has something to do with the moire. I did what I could to stress it ( output at zero quality, too) - but I couldn't get your checkerboard result. 1) Perhaps dropboxing the original raw, xmp, and your export settings - and we could see if we can replicate. 2) Is there some other 'gotcha' that might be involved. Is the output image you provided the actual image as opposed to a screenshot? Any other differences between how you handled this shot versus ones in the past? There's no way you could be printing a Smart Preview?
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