Trainers, reports are coming in that Niantic are changing Pokemon Go’s players’ username without any permission and without any previous notification.
There are many Pokemon Go players reporting that their in-game username/nickname is changed without their permission and Niantic and Pokemon Go are adding a number or a letter at the end of the current nickname.
Now, to make this clear for everyone, yes, they are changing/adjusting players’ nicknames and there is a reason for it. Niantic and Pokemon Go are changing players’ nicknames because it’s a DUPLICATE Trainer nickname.
Now, as per Niantic email, they want to avoid any confusion and if you don’t like your new nickname, you can always change it via the Settings menu in the game.
They will continue to be changing/adjusting players’ nicknames in the following weeks as well, so you might want to check your email daily.