Presumably this is because a block is different from the content being removed. It simply means the servers stop communicating with each other regarding new communities, posts and comments. This could allow the instance to be unblocked and the old content to continue existing – say for example when an instance has been acting badly, but it gets fixed some time later.

Blocked instances should probably not show up in search, but if you have a direct link to an old post, perhaps this should still be available? Not being able to block a community when its instance is already blocked makes sense, and probably doesn’t matter if you mostly check for new content, but I can see it being a bother when its shows up in other situations. One could call this a bug, or an oversight, but I suppose it depends on what the intended result is.

Common cause for that issue is you mixing up the website/forum account details with your game account ones. Unfortunately those are separate. If you got the game from itch/Humble you should’ve gotten an email with instructions to set up your game account, if I recall, and you’d download it from there, rather than the website? Feel free to poke support if you’re not able to get things working.