I'm not sure where the guys are right now or if you still having that issue but it is likely related to the CDN news from a few days ago, which seems to be the cause for some other issues too.
Did this break federation with lemmynsfw? I just noticed a lack of certain posts on /all, and after double checking it seems there hasn't been anything federated for 4 days. https://fedia.io/d/lemmynsfw.com/
You generally seem to need to have at least 1 account from that instance subscribed to your magazine for federation to kick in (which then still can take a bit of time). Same works the other way around. The unfortunate thing is that you kinda have to use external community / magazine indexers to search for them, unless you know the exact name & instance domain they're in, since a search won't find non indexed ones by itself.
Imo one of the largest issues regarding the fediverse.
That makes no sense to me. Imagine blocking users would work the same way and it would just remove links to their profile, but not the stuff the account posts.
It definitely does not block threads from those instances showing up. For example I have lemmy.ml blocked that way and I still get the occasional lemmy.ml threads pop up and have to manually block all the different communities on that instance.
Blocking instances on kbin / mbin does not work though. You will still see the communities threads & users (and getting to that page in the first place is a hassle too since there's no link to it).