One thing I've noticed on my travels around various #instances is that not all instances are visible on all instances. And I don't think it's because those instances have been blocked. I think it's just one of those not-worky things #computer type things do for no reason.
@lydiaconwell It isnt that either, its how federation works. One instance wont federate with another until there is at least one user on the server following a user from the other.
If that is already the case then it is likely a block.