The title pretty much sums it up. We're all part of a Server, and we all create characters under one campaign as an unassigned character, before assigning them to the various other campaigns of the server. Only difference is - mine can't. They don't show up at all after hitting the Invite Links. The only time they showed up is if I pop back into Campaign A. Claim them, then hit Invite Link to Campaign B, then they show up as Greyed Out.

And according to everyone on the server, I'm the only one with this issue.

Any help?

You must A) have claimed the character (or else it won’t count as yours), and B) take that character and leave the campaign with it. If a character is already in one campaign then they can’t join another one. Once you take the character out of the first campaign it will no longer be greyed out and you’ll be able to join the second campaign with it. I guarantee you that “everyone on the server” who didn’t have a problem did it that way, and they just didn’t mention the required steps because they assumed you knew.