I see a different pattern than I see in your screenshot which makes sense with different instance/client. What's weirder is the pattern I see today is different than I saw when I first saw the thread. I thought lemmy saved a thumbnail for the image. It makes sense different instances would have different settings for the thumbnail which causes different patterns, but I wonder why my instance's thumbnail changed over time?

Thumbnail shouldn't have regenerated and even if it did the generation should be deterministic with a more or less identical outcome. Unless the thumbnail is quite high resolution, the browser/app scaling the thumbnail down again on the fly a second time wouldn't cause the pattern to change much... Maybe I first viewed it before thumbnail was fully generated or maybe lemmy stores multiple thumbnails at different resolutions?