kbin did not defederate with .world, and beehaw hasn't defederated yet with kbin (although I guess sooner or later they will) so I do not know what you are talking about. In any case, this has nothing to do with the ability or inability to see the site, which on my end works fine btw.
Yesterday kbin removed that restriction, and now they are fully federated with lemmy. But I don't know if all "magazines" (kbin communities) are fully synchronised, a couple I was following finished to synchronise only this morning.
https://browse.feddit.de works only for Lemmy's instances and communities, so if you want something more precise than your instance's search bar you should go to https://kbin.social/magazines and then copypaste the link to your instance (in your case feedly.j-cloud.uk ) search bar if you want to subscribe to it.
In all cases, Kbin is different form Lemmy if seen from its own site, since they are trying to do a more comprehensive social platform, while instead Lemmy is just trying to be a link aggregator (The same typology of Reddit and of other now defunct sites). So, to summarise up, from lemmy you can see all the contents of kbin (which is a different software) but the "experience" is different from the one you have on the kbin site and thus, functionally, when using a lemmy instances kbin can be treated as another lemmy instance, even if it isn't.
@Habnab lol as a --day walker vampire-- er geek. I think I got the: <s> good one! you defederated from life.llolololololololol especially on fridays. I have to get my house of the dead and --violent porn- er anime and (caugh) totallynothentai(caugh) on
They don't have the beefiest server ever, although most lemmy instances don't. I experienced that 404 page and a 502 page a few times over the last few days, there are just random moments, possibly due to high traffic, where it became inaccessible for a few minutes at a time.
Old posts and comments will be seen, new ones won't be seen. One-sided defederation is like two linked servers delinking from one another - you keep the old info but you basically desync and one side can't see the other if they add new stuff.
That's why I have accounts on both kbin and l.world - so that I am able to access more information as it gets updated. It seems the influx of new users is leading to a fracturing and a defederation of the biggest instances, so having one account for all of the threadiverse is not viable.
Please don't spread rumors like this, it's not true. There are several kbin instances in their linked instances column and none of them are blocked, including kbin.social.