Kbin is very young software. The dev was doing really well, then /u/spez dumped 10-bajillion users on it. I'm surprised the servers are still operating.
Lemmy's a lot more mature, but it's never been tested with this kind of traffic. It's impressive that any of these sites are still going. I'd give it at least another month until things settle, adjustments are made, instances update, et c. et c.
Kbin is still having some issues with federation, they can access Lemmy just fine but we have some issues connecting to their magazines. Sometimes it works, but the admin there is working hard to fix it.
I had the same issue browsing a lemmy.world community from kbin.social, looks empty to me from kbin except for this message:
The magazine from the federated server may be incomplete. Browse more on the original instance.
So I checked the original instance and there were already some threads there, then I created a new thread from kbin and it worked, it appears on both kbin and lemmy, but from kbin I still can only see my own thread, not the rest.
Oh well, I guess it's a matter of time, @ernest is working really hard to fix everything and so far apart from a couple of things it has been a pretty smooth experience for me.