I wonder if they are behind from the downtime, following your instructions works, but the page is just empty. I guess, maybe I just need to wait. The other communities loaded the first 20 posts or so immediately.
Yeah once you subscribe it should show all new content going forward. The other communities you tried has probably already been added by me or someone else. I have a bunch in my watch list waiting for federation.
I think that Cloudflare problem was fixed recently, since now I can see kbin.social stuff on Beehaw's front page when browsing All, eg. https://beehaw.org/c/fediverse@kbin.social