Important to note that’s not necessarily Kbin. Some of the major instances of Lemmy had an issue where they were blocking inbound Kbin traffic but allowing their traffic out.
It was unclear if it was somehow intentional or the result of a bug in their most recent upgrade.
I don’t thinks that’s accurate, Kbin has only co-existed for a few Lemmy versions. I’ve been on Kbin before the initial wave of new users, when the site had about 200 users, federation was fine. You may be thinking of when federation was deliberately broken by Ernest with the entire fediverse for about a week when he had to enable Cloudflare DDOS protection during the first surge of signups.
The specific issue here was highlighted by a Kbin user several days ago. They monitored the traffic back and forth and saw that inbound Kbin-bot requests were denied by Lemmy.ml after the latest upgrade. At the time of that post, Lemmy.world did not have the issues and it had not upgraded yet. I’m not sure if that issue has since been fixed in the code or not.