I can see recent (few hours ago) comments of mine on lemmy.world (and kbin.social is in the linked instances list), so it doesn't look like it actually stopped federating. But yeah, I can't access kbinmeta from over there.
edit: I think I've read, back when ernest was gone, about some big Lemmy instance blocking kbin.social magazine federation because of the bot spam in so many magazines. I assumed it's just rumors, but is it actually real and still a thing lemmy.world is doing?