Communities only appear on this instance if they've already been discovered by somebody. If you get a 404 error, try pasting "!community_name@home.instance.name" into the community search field. It'll say "no results" but it'll actually fetch the community and then you can subscribe.
Sometimes it still just randomly doesn't work though.
I've been having a devil of a time trying to view new communities to subscribe to them. I just keep getting 404 errors.
Communities only appear on this instance if they've already been discovered by somebody. If you get a 404 error, try pasting "!community_name@home.instance.name" into the community search field. It'll say "no results" but it'll actually fetch the community and then you can subscribe.
Sometimes it still just randomly doesn't work though.