Can you please elaborate for which background are you referring to?

https://www.worldanvil.com/w/transformers3A-united-ratha The background for this is supposed to be this- https://www.worldanvil.com/i/5275762 -but it's not loading for any theme.

Backgrounds work in other worlds, but not this one.

That sounds like there is an overload on the theme that you are using or that there is custom CSS that overrides it.

I don't have any custom CSS for this world. I've checked with all the themes, and it seems like Modern Spaceships is the only one that loads the background image I want. I've used the exact same background image in several of my other worlds before, and it's worked perfectly fine.

I am really sorry but I do know what to tell you - which themes are your other worlds use?

The other worlds that use that background use Area 51, Stars, Modern spaceships, Your World Darkly, and the default theme.

And using the same theme and the same image does not work on the world in question? I am sorry but the only thing remaining is custom CSS and you have none - I am not sure what to say

I've just tried creating a new world with nothing in it to test, and the same thing happened. I've also tried it on a different computer, and it's still not showing the background image.

Further testing has shown apparently it's just that particular image that's causing trouble. I've uploaded other images to use as backgrounds, and each one has worked just fine.

In which case I'd say it's on the image and not WA :)