Vue is not rendered in Capybara test

I'm trying to test Vue.js from Rspec with Capybara. My problem is: the body is empty.

I was looking info for a few days and all the solutions is to change the driver of Capybara. I tried all but the bug persists.

My rails_helper.rb

# This file is copied to spec/ when you run 'rails generate rspec:install'
require 'spec_helper'
ENV['RAILS_ENV'] ||= 'test'
require File.expand_path('../../config/environment', __FILE__)
# Prevent database truncation if the environment is production
abort("The Rails environment is running in production mode!") if Rails.env.production?
require 'rspec/rails'
# Add additional requires below this line. Rails is not loaded until this point!
require 'capybara/poltergeist'
require 'factory_girl_rails'
require 'capybara/rspec'

options = {js_errors: false}

Capybara.server = :puma
require 'rack_session_access/capybara'
require 'capybara/poltergeist'

RSpec.configure do |conf|
  conf.include FactoryGirl::Syntax::Methods
end

Capybara.register_driver :poltergeist do |app|
    Capybara::Poltergeist::Driver.new(app, options)
end
Capybara.javascript_driver = :poltergeist
# Requires supporting ruby files with custom matchers and macros, etc, in
# spec/support/ and its subdirectories. Files matching `spec/**/*_spec.rb` are
# run as spec files by default. This means that files in spec/support that end
# in _spec.rb will both be required and run as specs, causing the specs to be
# run twice. It is recommended that you do not name files matching this glob to
# end with _spec.rb. You can configure this pattern with the --pattern
# option on the command line or in ~/.rspec, .rspec or `.rspec-local`.
#
# The following line is provided for convenience purposes. It has the downside
# of increasing the boot-up time by auto-requiring all files in the support
# directory. Alternatively, in the individual `*_spec.rb` files, manually
# require only the support files necessary.
#
# Dir[Rails.root.join('spec/support/**/*.rb')].each { |f| require f }

RSpec.configure do |config|
  # RSpec Rails can automatically mix in different behaviours to your tests
  # based on their file location, for example enabling you to call `get` and
  # `post` in specs under `spec/controllers`.
  #
  # You can disable this behaviour by removing the line below, and instead
  # explicitly tag your specs with their type, e.g.:
  #
  #     RSpec.describe UsersController, :type => :controller do
  #       # ...
  #     end
  #
  # The different available types are documented in the features, such as in
  # https://relishapp.com/rspec/rspec-rails/docs
  config.infer_spec_type_from_file_location!

  # Filter lines from Rails gems in backtraces.
  config.filter_rails_from_backtrace!
  # arbitrary gems may also be filtered via:
  # config.filter_gems_from_backtrace("gem name")

  config.include FactoryGirl::Syntax::Methods # this allows to use factory girl gem's methods
  # this is to test javascript with capybara  
end

Then I have a feature test in spec/features/

require 'rails_helper'
require 'support/login_helper'

RSpec.feature "login", type: :feature, js: true do
  include LoginHelper

  before do
    login!
  end

  scenario 'a' do
    expect(true).to eq(true)
  end
end

And finally, my login helper when I have the error.

require 'rails_helper'

module LoginHelper
    def login!
        visit root_path
        print page.html
        fill_in "username", with: "aaa"
        click_button "Entrar"
    end
end

In the helper I try to visit the root_path, get the input and then fill with some mock data.

In the console, the test provides me the following error:

Failure/error: fill_in "username", with: "aaa"

Capybara::ElementNotFound:
   Unable to find visible field "username" that is not disabled

I print the page.html before the fill_in and I have

In the vue.app I'm using