We first got a report of this around this time last month, but have received significantly more reports due to such a frequently seen asset being affected.
This is a unique to Roblox issue and has been brought up before. Roblox has been experimenting with image compression it seems. Further, given the nature of the game, Adopt Me assets are rather likely to be memory efficient (i.e. certainly not massively upscaled for no reason and then downscaled, because that would hurt mobile very badly). Also, if you look at the images, they have very clear compression artifacts, not blurring, pixilation, or downscaling artifacts. Not sure why you’d assume something so silly.
I’ve had this exact same issue except quality is inconsistent across ALL devices, mobile or not. I’ve been trying to figure out what the common denominator is but it’s seemingly random.