lemmy.ml is blocking kbin requests, meaning kbin instances get an error when trying to retrieve new posts and comments.
It's still unclear why they are doing it, but it seems to be deliberate as they are specifically blocking the kbin user agent (some text kbin uses to identify itself to other fediverse servers).
I assume they're trying to defederate without actually limiting the freedom of their own users. By just blocking requests from kbin instances, their own users can still use kbin magazines as they please, only kbin users are excluded from federation.