The community banner and icon are both broken and seem to be hosted away from Lemmy World on fry.gs which I believe is/was the home instance for one of the original mods. That instance appears to be no longer functional.
Not sure how long they've been broken; I just noticed that when I flushed my cache recently they weren't working and then realized the banner and icon links the API returns no longer work.
"icon": "https://fry.gs/pictrs/image/c6832070-8625-4688-b9e5-5d519541e092.png",
"banner": "https://fry.gs/pictrs/image/1a1e9226-87cb-4499-94a7-d43b1e520e50.png",
Update: I did find the banner. ~~I don't have a copy of the banner~~, but I do have the icon in my instance's proxy/cache if you want to save it and re-apply it from Lemmy World.
Icon
Banner
You are so helpful, I for one find that fucking awesome! ๐