Transferring from team account to team account won't work. (BB-9510)
If you're logged in as a team account, and you attempt to transfer a repository to another team account, no one will receive the transfer notification. This is because users aren't meant to be logged in to the team account.
To workaround this, ensure both teams have an Administrator. Then, while logged in as a team administrator, transfer the repository to the other team. All notifications should be sent.