Sorry for my English
1. There is an account with a linked Google play
2. Send GooglePlayConnectRequest with new account Google Play
3. Response - error " ACCOUNT_ALREADY_LINKED", (switchIfPossible - false)
4. Result - GS.GSPlatform.UserId == "empty"
Also, if there are two accounts with a linked Google Play (switchIfPossible - true) , when switching between them sometimes -result GS.GSPlatform.UserId == "empty", also at this time...
GS.GameSparksAuthenticated += delegate(string _userId)
playerId = _userId;
// userId == empty
But in the Cloud Code you can get playerId