Yeah, using that link, you're viewing lemmy.world's fediverse comm but you're viewing it from the feddit.nl instance. From lemmy.world itself, the link to that comm would be https://lemmy.world/c/fediverse. The post we're talking about is visible from those places, as it should be. If hexbear were federated with .world, the link for us would be http://hexbear.net/c/fediverse@lemmy.world, but that doesn't work since we aren't federated. Since lemmy.ml is federated with lemmy.world, the following is the link to the same comm from lemmy.ml: https://lemmy.ml/c/fediverse@lemmy.world However, you'll notice that the post in question "Lemmy.ml tankie censorship problem" is not visible from that link. Which means that everyone logged in and using lemmy.ml do not see that post. It doesn't exist as far as they're concerned, since the only way to see it would be to do so from an instance that is not their own, which people are not liable to go looking for since they aren't aware of what they can't see. I don't know if instances can make certain posts inaccessible to other instances (never heard of that, but maybe?), but whether it was done intentionally or is just a lemmy bug, the effect is the same.

I hope that made sense, and I apologize if I was just explaining a bunch of stuff you already know. Just trying to clarify the issue and explain it in case others are confused.