From other posts, it's apparently just poor AVIF support on some device/app.

Personally, I think it may be bad AVIF encoding based on who uploaded the image. I only see the glitched images from .world posts. That makes me think it's some sort of combo of a particular user app and either the .world instance or other users' instances caching the images. (For example, every image I see is actually rehosted on the lemmy.zip servers)