MongoError: E11000 duplicate key error collection when trying to Log In - node.js

Question

I logged in with google in my app without problems, I logged out and when logged in again I got this error:
"MongoError: E11000 duplicate key error collection: myAppDB.users index: username_1 dup key: { username: "John Doe" }"
I'm not creating a new user with the same name, I'd just need to log in.
App.js
mongoose.set("useCreateIndex", true);
const userSchema = new mongoose.Schema({
googleId: String,
profileImage: String,
myCollection: {
type: Object,
default: Object
},
games: {
type: Object,
default: Object
}
});
userSchema.plugin(passportLocalMongoose);
userSchema.plugin(findOrCreate);
const User = new mongoose.model("User", userSchema);
passport.use(new GoogleStrategy({
clientID: process.env.CLIENT_ID,
clientSecret: process.env.CLIENT_SECRET,
callbackURL: "http://localhost:3000/auth/google/myApp",
userProfileUrl: "https://www.googleapis.com/oauth2/v3/userinfo",
passReqToCallback: true
},
function(req, accessToken, refreshToken, profile, cb) {
console.log(profile);
User.findOrCreate({
googleId: profile.id,
username: profile.displayName,
profileImage: profile.photos[0].value,
myCollection: catalogDb,
games: {}
},
function(err, user) {
return cb(err, user);
});
}
));
passport.use(User.createStrategy());
passport.serializeUser(function(user, done) {
done(null, user.id);
});
passport.deserializeUser(function(id, done) {
User.findById(id, function(err, user) {
done(err, user);
});
});