So you move a shared mailbox from Exchange to either a new server or to Office 365. After, a user still sees a shared mailbox automapped to their profile due to the exchange automapping feature. You aren't able to map the moved mailbox to their profile.
An easy solution is to simply remove it from the attributes in Active Directory.
- Open Active Directory Users and Computers.
- Click the View menu and select Advanced Features.
- Open the user in question.
- Click on the Attribute editor tab.
- Scroll down to msExchDelegateListLink, open it.
- Remote the mailbox that is automapped.