kbin.social shows up in the instances list (https://discuss.tchncs.de/instances), but I’m having trouble with !nfl@kbin.social. I couldn’t get it to show up in search until I searched for the full URL (https://kbin.social/m/nfl). Once it did, I can join, but there’s no content. See here: https://discuss.tchncs.de/c/NFL@kbin.social
Edit: actually, one post has now shown up, but not the rest.
That’s not been true for me joining communities on other Lemmy instances.
Have you joined communities that someone was already subscribed to before you, or were you also the first person to add these communities to your instance? Otherwise I don’t know, that’s how I saw it behave but it could be just bugs or too much traffic.
When I joined the !knitting@lemmy.world I was definitely the first person to join. E.g. I got an error going to https://discuss.tchncs.de/c/knitting@lemmy.world until I did the search. But once I did the search it worked, I could follow I had immediate content etc.