Impossible leaderboard entries

Dear Community

I have published a new game on Google Play. When starting the game, it is mandatory to enter your own player name - otherwise the player cannot start the game.

Nevertheless, I have entries “PLAYER12345” in the leaderboard - i.e. automatically generated names.

There is no error in the code, because the leaderboard entry uses the corresponding global variable.

Do any of you have any idea why I still have such entries?