Issue:
In Exchange Management Console - Under recipient configuration you disconnected 1 mailbox and tried to reconnect. When you check on Disconnected mailbox you cannot view the user you just disconnected.
FYI, under disconnected mailbox - in action pane I need to connect to server "use your mailbox virtual name if it's CCR cluster" However, the user may not appear in Disconnected Mailbox yet.
Solution: Go to management shell and type the following:
Get-MailboxDatabase | Clean-MailboxDatabase
Then refresh view on DisconnectedMailboxes and it should appear
