@feditips @_dunnster there's two things happening here: 1. images with no alt text get that border if browsed on toot.wales 2. our host has a media cache setting that removes old media - which is then re-requested upon demand.
It looks like the re-requests are getting queued and taking up to a minute to get re-delivered from the remote server in some cases.
I suggest scrolling more slowly :o) - or opening the original page (three dot menu) if you need to see the image more quickly