The same pics showing up as group avatars on completely different sites

I have two different websites. Both use different hosts (although both domains are registered and hosted at the same location). I am having the same group pics showing up on both sites when I set it up on just one of them. For example, I might set a particular pic as the avatar for a group on one site, and it will replace the avatar on the other site of a completely random and unrelated group.

Can anyone think of a reason why this would be happening and how I can fix it? I’ve checked it on multiple different browsers and I get the same result.