For our game, we use Facebook id to get player's friend list to send invites or post shares, and that's all. So if a player created multiple Playfab ids and link them to the same Facebook id, it's okay. I know for some games this is a bug. But for us, it's actually kind of making sense to do it this way.
In your case, you are using Facebook to log into the account. Since there would be no way to figure out which account is the correct one if more than one were to be linked, only one PlayFab account may be linked to one Facebook account.
We only use PlayFabClientAPI.LoginWithIOSDeviceID to log into the game, so this won't be a problem for us. Maybe in the future you guys can provide some kind of settings to let us control how to log into the server, and which account is the main account. Thanks for your quick support!
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