webpacker: Styles not loaded after upgrade to Rails 6 / Bundler 2

Hello, this may be a little weird but we’re using Rails 6 beta2 for our project, everything was fine but just after we upgraded to bundler 2 styles are not loading anymore in our app.

This is our app structure for webpack:

├── javascript
│   ├── application
│   │   ├── javascripts
│   │   │   └── index.js.erb
│   │   └── stylesheets
│   │       ├── _variables_override.scss
│   │       ├── application.scss
│   │       ├── components
│   │       │   ├── _flash.scss
│   │       │   ├── _footer.scss
│   │       │   ├── _forms.scss
│   │       │   ├── _header.scss
│   │       │   └── index.scss
│   │       ├── index.js.erb
│   │       └── modules
│   │           ├── _base.scss
│   │           ├── _layout.scss
│   │           └── index.scss
│   └── packs
│       └── application.js

Inside packs/application.js:

import '../application/stylesheets/index.js.erb';
import '../application/javascripts/index.js.erb';

and our webpacker.yml :

# Note: You must restart bin/webpack-dev-server for changes to take effect

default: &default
  source_path: app/javascript
  source_entry_path: packs
  public_output_path: packs
  cache_path: tmp/cache/webpacker

  # Additional paths webpack should lookup modules
  # ['app/assets', 'engine/foo/app/assets']
  resolved_paths: []

  # Reload manifest.json on all requests so we reload latest compiled packs
  cache_manifest: false

  extensions:
    - .js
    - .sass
    - .scss
    - .css
    - .module.sass
    - .module.scss
    - .module.css
    - .png
    - .svg
    - .gif
    - .jpeg
    - .jpg

development:
  <<: *default
  compile: true

  # Reference: https://webpack.js.org/configuration/dev-server/
  dev_server:
    https: false
    host: localhost
    port: 3035
    public: localhost:3035
    hmr: false
    # Inline should be set to true if using HMR
    inline: true
    overlay: true
    compress: true
    disable_host_check: true
    use_local_ip: false
    quiet: false
    headers:
      'Access-Control-Allow-Origin': '*'
    watch_options:
      ignored: /node_modules/


test:
  <<: *default
  compile: true

  # Compile test packs to a separate directory
  public_output_path: packs-test

staging:
  <<: *default

  # Production depends on precompilation of packs prior to booting for performance.
  compile: false

  # Cache manifest.json for performance
  cache_manifest: true

production:
  <<: *default

  # Production depends on precompilation of packs prior to booting for performance.
  compile: false

  # Cache manifest.json for performance
  cache_manifest: true

and layout file:

!!!
%html
  %head
    %meta{ :content => "text/html; charset=UTF-8", "http-equiv" => "Content-Type"}/
    %meta{ :content => "width=device-width, initial-scale=1", name: "viewport" }/
    %title= t("website_title")
    = csrf_meta_tags
    = csp_meta_tag
    = stylesheet_pack_tag "application", media: "all", "data-turbolinks-track": "reload"
    = javascript_pack_tag "application", "data-turbolinks-track": "reload"

    - if Rails.env.development?
      :css
        .translation_missing { color: red !important; }

  %body{ class: controller_name }
    .absolute-wrapper
      = render "shared/header"

      .content-wrapper
        = render "shared/flash"

        .content
          = yield

      = render "shared/footer"

Can someone tell me if I’m missing something? Before upgrading to bundler 2 everything was working fine!