why mongoose query works fine on localhost but not on prod server instead returns an empty []?

So i have a few days trying to debug my restful API, specifically mongoose and MongoDB on prod server (aws server). There is a service which query Users collection and returns the model, simple enough. But the question is this why would this query criteria return an empty [] on prod server but returns the model on localhost and using Postman for testing purposes.On prod server i will have to be explicit on what data i want from the document in order to return the model. Below i will leave my codebase such as the schema, services.

NOTE -> my prod server and local machine are both Ubuntu. Prod server (Ubuntu 18.04.3, codename Bionic) and local machine (Ubuntu 21.10, codename Impish).

Schema

userSchema: {
name: {
    type:Schema.Types.String,
    required: true
  },
carsOwned: [{
    name: {
      type: Schema.Types.String,
    },
    brand: [{
      name: {
        type: Schema.Types.String,
      },
    }]
  }],
totalNumberOfCarsOwned: {
    type: Schema.Types.Number,
    default: function () {
      let carsCount = 0;
      for (let car of this.carsOwned) {
        carsCount += car.brand.length;
      }
      return carsCount
    }
}

Sevice

userService.getCarById = (id) => {
// this is the original query which works perfectly locally but not on live server (aws)
  return userModel.findOne({carsOwned: {$elemMatch: {_id: id}}})

// This is the updated query which works perfectly both locally and live server (aws)
  return userModel.findOne({carsOwned: {$elemMatch: {_id: id} } }, {"carsOwned._id":1, "carsOwned.brand":1 });

// noticed how i exclude totalNumberOfCarsOwned in the updated query criteria. If i included the property totalNumberOfCarsOwned then it returns an empty array like user = []
};

Both versions of my MongoDB (5.0.8) and Mongoose(5.4.16) are the same locally and on prod server. I simply don't understand why others query works fine and this is the only service that has a tricky and weird temporary solution.

I just need an guide that points me to an answer that explain this issue, please.