Yeah I'm not sure, but I think feddit.de just region blocks any IP addresses not in Germany, which is honestly really frustrating and doesn't play nicely with the fediverse.
Catbox is blocked in many regions, including Australia, Britain, and Ireland; something they explain on their FAQ page (archive link to bypass any such restrictions, though their non-files domain probably should work anyway). Bizarrely, New Zealand is not on that list, despite a shooting in NZ being cited as the reason it's blocked in Australia. It's easy to bypass in some regions; harder in others.
Anyway, this image loaded for me just now, on lemmy-ui. Dunno if it was a client issue, a network issue, or something else.
edit: OH WAIT! I just realised that this image is a catbox one! That explains it. My phone doesn't have custom DNS set up which is what I have on my computer to bypass the catbox blocking. So it didn't load on my phone but does on my computer. Doh.