Why is only the first user saved in the database?

Question

MongoDB

Faced with the problem that only the first user is saved to the database (when the database is empty), and all subsequent ones are not saved. I don't know, where is the problem?

router.post('/register',
  userController.validateRegister,
  catchErrors(userController.register)
)

controller

exports.validateRegister = (req, res, next) => {
  // from express-validator
  req.sanitizeBody('name')
  req.checkBody('name', 'You must supply a name!').notEmpty()
  req.checkBody('email', 'That email is not valid!').isEmail()
  // https://github.com/chriso/validator.js/
  req.sanitizeBody('email').normalizeEmail({
    // gmail_remove_dots: true,
    remove_dots: false,
    remove_extension: false,
    gmail_remove_subaddress: false
  })
  req.checkBody('password', 'Password cannot be blank!').notEmpty()
  req.checkBody('password-confirm', 'Confirmed password cannot be blank!').notEmpty()
  req.checkBody('password-confirm', 'Passwords do not match!').equals(req.body.password)

  const errors = req.validationErrors()
  if (errors) {
    req.flash('error', errors.map(err => err.msg))
    // repopulate filled fields if error
    res.render('register', { body: req.body, flashes: req.flash() })
    return // stop the function
  }
  next()
}

exports.register = async (req, res, next) => {
  const user = new User({ email: req.body.email, name: req.body.name })
  const register = promisify(User.register, User)
  await register(user, req.body.password)
  next()
}

passport.js

const passport = require('passport')
const mongoose = require('mongoose')
const User = mongoose.model('User')

passport.use(User.createStrategy())

passport.serializeUser(User.serializeUser())
passport.deserializeUser(User.deserializeUser())

model

const mongoose = require('mongoose')
const Schema = mongoose.Schema
mongoose.Promise = global.Promise
const md5 = require('md5')
const validator = require('validator')
const mongodbErrorHandler = require('mongoose-mongodb-errors')
const passportLocalMongoose = require('passport-local-mongoose')

const userSchema = new Schema ({
  email: {
    type: String,
    unique: true,
    lowercase: true,
    trim: true,
    validate: [validator.isEmail, 'Invalid email address!'],
    required: 'Please provide email address'
  },
  name: {
    type: String,
    required: 'Please provide a name',
    trim: true
  }
})

userSchema.plugin(passportLocalMongoose, { usernameField: 'email' })
userSchema.plugin(mongodbErrorHandler)

module.exports = mongoose.model('User', userSchema)

Answer 1

exports.register = async (req, res, next) => {
  const user = new User({ email: req.body.email, name: req.body.name }) 
  const register = promisify(User.register, User) это чей метод? bluebird? 
  await register(user, req.body.password) это аналог save? Какой запрос к базе тут делаете? 
  next()  <--- Что делает этот next? Какой следущий хендлер в цепочке? 
}

And they say callback is evil, let's figure out together what's going on here.