It seems that any Lemmy.world and Lemmy.ml hosted communities aren’t any longer federating properly via kbin as I started getting 404 errors on all of them. Examples:

https://lemmy.world/c/personalfinance: ok
https://kbin.social/m/personalfinance@lemmy.world: 404

https://lemmy.ml/c/fire: ok
https://kbin.social/m/finance@lemmy.ml: 404

https://beehaw.org/c/finance: ok
https://kbin.social/m/finance@beehaw.org: ok