When I visit an NPC shop, many, many of the items are very blurry.

I'm seeing this too. There's been a few. I'm pretty sure if it's blurry in one place, it's blurry everywhere. For example, three different times in the SubQ, the First Blood Boots have been blurry.

Trying to display it again here creates the same problem.

I opened the image in a new tab to see if that would make it load. To me it looked like it loaded partway and then got stuck, and a hard refresh in a new tab has often fixed things like slow avatars in the past for me. And I was quite surprised to find that the image is smaller than it should be! Looks like the resolution was changed, and it's blurry because it's been zoomed in to fit the usual item image size.

If this is the case for all the blurry items -- and I've seen a few, just can't recall what offhand -- then the problem with the image file is likely the cause. I have no idea why it's smaller, but it definitely is. ^.^