What's up with "The magazine from the federated server may be incomplete. Browse more on the original instance."? Is this working as intended or is it a bug?

I've been seeing this for quite a bit, and thought it'd resolve itself once CloudFlare was taken off, but I'm still seeing it on many external communities from e.g. Lemmy. Not all posts or comments are visible from Kbin. Any idea on what's going on?...