Repro script mongoose issue #9909

gistfile1.txt

const mongoose = require('mongoose');
mongoose.set('debug', true);

const connectionString = ``;
const { Schema } = mongoose;

run().then(() => console.log('done')).catch(error => console.error(error.stack));

async function run() {
  await mongoose.connect(connectionString);
  await mongoose.connection.dropDatabase();

  const thingSchema = new Schema({
    name: {
      type: String,
    },
    bookings: [{
      attests: [{
        user: {type:String},
        attest: {type:Boolean},
        comment: {type:String}
      }],
      ratings: [{
        user: {type:String},
        rate: {type:Number},
        comment: {type:String}
      }],
      cost: {type:Number},
      booking: {type:String}
    }],
    role: {
      required: true,
      type: String,
    },
    joinedAt: {
      type: Date,
    }
  });

  const Thing = mongoose.model('Thing', thingSchema);

  let newThing = new Thing({
    name:'theNewThing',
    role: 'boss',
    bookings: [{
      booking: 'tr87gew'
    }],
    joinedAt: new Date()
  });

  try { await newThing.save()
  }catch(e){ return console.log('error adding new thing',e) }

  // Get every session in the db
  let thing;
  try { thing = await Thing.findOne({_id:newThing._id}).select('name bookings');
  }catch(e){ return console.log('error finding thing',e); }

  thing.bookings[0].attests[0] = {
    user: 'bla',
    attest: true,
    comment: 'kakaka'
  }

  try { await thing.save()
  }catch(e){ return console.log('error adding new thing',e) }
}