Multiple friends that I've asked have been experiencing the same problem for a while. Here you can see my friend Christamyboat is online and right in front of me. Months ago I remember that friends that were online would have their usernames appear in green font. I've also noticed that if she's in the same lobby as me I can send her private messages by typing "/tell Christamyboat <message>" and she receives it. But if we're in different lobbies it will say "That player cannot be found" Here you can see that she appears offline in my list but she's online and right in front of me: When I change my settings to showing only friends in the lobby, you can see that it works but she still appears offline.