CKEditorのモジュール導入ができません「Uncaught CKEditorError: ckeditor-duplicated-modules」

Question

リッチテキストエディタCKeditor5を導入しているのですが、モジュール導入で解決しなかった為、ご相談させてください。

環境

webpackで導入しているのですが、package.jsonとwebpack.config.jsの中身は以下のとおりです。

//package.json
{
  "name": "sample_project",
  "version": "1.0.0",
  "scripts": {
    "build": "webpack --mode development"
  },
  "dependencies": {
    "@ckeditor/ckeditor5-alignment": "^27.1.0",
    "@ckeditor/ckeditor5-basic-styles": "^27.1.0",
    "@ckeditor/ckeditor5-block-quote": "^27.1.0",
    "@ckeditor/ckeditor5-dev-utils": "^24.4.2",
    "@ckeditor/ckeditor5-dev-webpack-plugin": "^24.4.2",
    "@ckeditor/ckeditor5-easy-image": "^27.1.0",
    "@ckeditor/ckeditor5-editor-decoupled": "^27.1.0",
    "@ckeditor/ckeditor5-essentials": "^27.1.0",
    "@ckeditor/ckeditor5-font": "^27.1.0",
    "@ckeditor/ckeditor5-horizontal-line": "^27.1.0",
    "@ckeditor/ckeditor5-image": "^27.1.0",
    "@ckeditor/ckeditor5-indent": "^27.1.0",
    "@ckeditor/ckeditor5-link": "^27.1.0",
    "@ckeditor/ckeditor5-list": "^27.1.0",
    "@ckeditor/ckeditor5-media-embed": "^27.1.0",
    "@ckeditor/ckeditor5-page-break": "^27.1.0",
    "@ckeditor/ckeditor5-paragraph": "^27.1.0",
    "@ckeditor/ckeditor5-remove-format": "^27.1.0",
    "@ckeditor/ckeditor5-table": "^27.1.0",
    "@ckeditor/ckeditor5-theme-lark": "^27.1.0",
    "@ckeditor/ckeditor5-upload": "^27.1.0",
    "@wiris/mathtype-ckeditor5": "^7.26.0",
    "postcss-loader": "^3.0.0",
    "raw-loader": "^3.1.0",
    "style-loader": "^1.3.0",
    "webpack": "^4.46.0",
    "webpack-cli": "^3.3.12"
  },
  "devDependencies": {
    "ckeditor5-math": "^28.0.0"
  }
}

//webpack.config.js
const path = require( 'path' );
const CKEditorWebpackPlugin = require( '@ckeditor/ckeditor5-dev-webpack-plugin' );
const { styles } = require( '@ckeditor/ckeditor5-dev-utils' );
module.exports = {
    entry: './src/index.js',
    output: {
        path: path.resolve( __dirname, 'dist' ),
        filename: 'bundle.js'
    },
    plugins: [
    new CKEditorWebpackPlugin( {
        language: 'ja',
    } ),
],
    module: {
//省略
};

確認できていること

今回導入したいモジュールがMathematicalと呼ばれるのなのですが、これを手順に従い導入する前に以下のindex.jsでは正しく動作が確認できております。

//index.js
import ClassicEditor from '@ckeditor/ckeditor5-editor-classic/src/classiceditor';
// import DecoupledEditor from '@ckeditor/ckeditor5-editor-decoupled/src/decouplededitor';
import Essentials from '@ckeditor/ckeditor5-essentials/src/essentials';
import Paragraph from '@ckeditor/ckeditor5-paragraph/src/paragraph';
import Table from '@ckeditor/ckeditor5-table/src/table';
import TableToolbar from '@ckeditor/ckeditor5-table/src/tabletoolbar';
import TableProperties from '@ckeditor/ckeditor5-table/src/tableproperties';
import TableCellProperties from '@ckeditor/ckeditor5-table/src/tablecellproperties';
import Font from '@ckeditor/ckeditor5-font/src/font';
import Bold from '@ckeditor/ckeditor5-basic-styles/src/bold';
import Italic from '@ckeditor/ckeditor5-basic-styles/src/italic';
import Underline from '@ckeditor/ckeditor5-basic-styles/src/underline';
import Strikethrough from '@ckeditor/ckeditor5-basic-styles/src/strikethrough';
import Code from '@ckeditor/ckeditor5-basic-styles/src/code';
import Subscript from '@ckeditor/ckeditor5-basic-styles/src/subscript';
import Superscript from '@ckeditor/ckeditor5-basic-styles/src/superscript';
import Alignment from '@ckeditor/ckeditor5-alignment/src/alignment';
import ListStyle from '@ckeditor/ckeditor5-list/src/liststyle';
import Indent from '@ckeditor/ckeditor5-indent/src/indent';
import IndentBlock from '@ckeditor/ckeditor5-indent/src/indentblock';
import BlockQuote from '@ckeditor/ckeditor5-block-quote/src/blockquote';
import Link from '@ckeditor/ckeditor5-link/src/link';
import AutoLink from '@ckeditor/ckeditor5-link/src/autolink';
import MediaEmbed from '@ckeditor/ckeditor5-media-embed/src/mediaembed';
import Image from '@ckeditor/ckeditor5-image/src/image'
import ImageInsert from '@ckeditor/ckeditor5-image/src/imageinsert';
import Base64UploadAdapter from '@ckeditor/ckeditor5-upload/src/adapters/base64uploadadapter';
import ImageToolbar from '@ckeditor/ckeditor5-image/src/imagetoolbar';
import ImageCaption from '@ckeditor/ckeditor5-image/src/imagecaption';
import ImageStyle from '@ckeditor/ckeditor5-image/src/imagestyle';
import ImageResize from '@ckeditor/ckeditor5-image/src/imageresize';
import LinkImage from '@ckeditor/ckeditor5-link/src/linkimage';
import HorizontalLine from '@ckeditor/ckeditor5-horizontal-line/src/horizontalline';
import PageBreak from '@ckeditor/ckeditor5-page-break/src/pagebreak';
import RemoveFormat from '@ckeditor/ckeditor5-remove-format/src/removeformat';


ClassicEditor
  .create( document.querySelector( '.document-editor__editable' ), {
    plugins: [
      Font//...中略

    ],
    toolbar: {
      items: ['fontSize'//...中略
            ]
    },
 //中略
    language: 'ja',
    // placeholder: 'テキストを編集してください'
  } )
  .then( editor => {
    const toolbarContainer = document.querySelector( '.document-editor__toolbar' );
    toolbarContainer.appendChild( editor.ui.view.toolbar.element );
    window.editor = editor;
  } )
  .catch( error => {
    console.error( error );
  } );

こちらを上記の手順に以下の様に実行しています
0. npm install ckeditor5-math --save-devで所定のディレクトリにインストール（正しく実行確認済）

1. index.jsに以下の//追加箇所を追加

//index.js
import ClassicEditor from '@ckeditor/ckeditor5-editor-classic/src/classiceditor';
// import DecoupledEditor from '@ckeditor/ckeditor5-editor-decoupled/src/decouplededitor';
import Essentials from '@ckeditor/ckeditor5-essentials/src/essentials';
import Paragraph from '@ckeditor/ckeditor5-paragraph/src/paragraph';
import Table from '@ckeditor/ckeditor5-table/src/table';
import TableToolbar from '@ckeditor/ckeditor5-table/src/tabletoolbar';
import TableProperties from '@ckeditor/ckeditor5-table/src/tableproperties';
import TableCellProperties from '@ckeditor/ckeditor5-table/src/tablecellproperties';
import Font from '@ckeditor/ckeditor5-font/src/font';
import Bold from '@ckeditor/ckeditor5-basic-styles/src/bold';
import Italic from '@ckeditor/ckeditor5-basic-styles/src/italic';
import Underline from '@ckeditor/ckeditor5-basic-styles/src/underline';
import Strikethrough from '@ckeditor/ckeditor5-basic-styles/src/strikethrough';
import Code from '@ckeditor/ckeditor5-basic-styles/src/code';
import Subscript from '@ckeditor/ckeditor5-basic-styles/src/subscript';
import Superscript from '@ckeditor/ckeditor5-basic-styles/src/superscript';
import Alignment from '@ckeditor/ckeditor5-alignment/src/alignment';
import ListStyle from '@ckeditor/ckeditor5-list/src/liststyle';
import Indent from '@ckeditor/ckeditor5-indent/src/indent';
import IndentBlock from '@ckeditor/ckeditor5-indent/src/indentblock';
import BlockQuote from '@ckeditor/ckeditor5-block-quote/src/blockquote';
import Link from '@ckeditor/ckeditor5-link/src/link';
import AutoLink from '@ckeditor/ckeditor5-link/src/autolink';
import MediaEmbed from '@ckeditor/ckeditor5-media-embed/src/mediaembed';
import Image from '@ckeditor/ckeditor5-image/src/image'
import ImageInsert from '@ckeditor/ckeditor5-image/src/imageinsert';
import Base64UploadAdapter from '@ckeditor/ckeditor5-upload/src/adapters/base64uploadadapter';
import ImageToolbar from '@ckeditor/ckeditor5-image/src/imagetoolbar';
import ImageCaption from '@ckeditor/ckeditor5-image/src/imagecaption';
import ImageStyle from '@ckeditor/ckeditor5-image/src/imagestyle';
import ImageResize from '@ckeditor/ckeditor5-image/src/imageresize';
import LinkImage from '@ckeditor/ckeditor5-link/src/linkimage';
import HorizontalLine from '@ckeditor/ckeditor5-horizontal-line/src/horizontalline';
import PageBreak from '@ckeditor/ckeditor5-page-break/src/pagebreak';
import RemoveFormat from '@ckeditor/ckeditor5-remove-format/src/removeformat';
import Mathematics from 'ckeditor5-math/src/math';//追加

ClassicEditor
  .create( document.querySelector( '.document-editor__editable' ), {
    plugins: [
      Font, Mathematics//追加

    ],
    toolbar: {
      items: ['fontSize',//中略
              'math'//追加
            ]
    },
//中略
    math: {//追加
    engine: 'mathjax',
    lazyLoad: undefined,
    outputType: 'script',
    forceOutputType: false,
    enablePreview: true,
    previewClassName: [],
    popupClassName: []
    },
//上記と同様のため後略

エラー

その結果、以下のエラーが出力されておりどうしても実装できません。
Uncaught CKEditorError: ckeditor-duplicated-modules
Uncaught ReferenceError: editor is not defined

GitHub上で公式のエラーに関連する投稿などもみたのですが、本モジュール導入に関するものを見つけることができず、八方塞がりになってしまった為、どなたか同じ様な経験や知見を持っている方にご相談させていただきたく投稿させていただきました。
よろしくお願い申し上げます。