So I've discovered a bit of a serious issue with the gamecenter login.
Sometimes (And I don't yet know why) the teamPlayerId for Game Center sometimes receives the id of 'Unavailable Player Identification' (see: https://developer.apple.com/forums/thread/683668)
Playfab is then treating all these players as the same player, and linking their accounts together.
So now we have one super user in our game who is an amalgamation of at least 1000+ players.
Can playfab please immediately stop authenticating players with an unavailable ID ?