My problem is that I need to enable the keychain sharing feature to App ID in order to make Facebook login work for iOS10. How to use Facebook iOS SDK on iOS 10
However,
Restarting the xcode fixes the issue ! I hate you apple :)
Go to the "general" tab and look at the "signing" section. I had been signed in at a Corporate account (which has since expired) and so had to select my correct account from the "Team" drop-down menu. Now the Team can be found in the Account.