After forking a sandbox we can download the whole project by hovering over main menu at top left and click download sandbox :

I'm not sure how this project is configured but I advise you to convert it to a default @vue/cli setup.

npm install && npm install -D @vue/cli-service @vue/cli-plugin-babel vue-template-compiler postcss-import postcss-url && npm install core-js

Edit .babelrc so it just contains:

{
  "presets": ["@vue/cli-plugin-babel/preset"]
}

• Create public folder and move index.html in it.
• Create src folder then move App.vue and index.js into it
• Rename index.js to main.js
• Edit main.js to replace template: '<App/>', components: { App } by render: h => h(App)
• Delete build and config folders

Edit package.json to add

"scripts": {
  "serve": "vue-cli-service serve",
  "build": "vue-cli-service build"
}

And run either npm run serve or npm run build

Also, in App.vue :

• Replace :key="office.id" by :key="'office' + office.id"
• Replace :key="factory.id" by :key="'factory' + factory.id"
• Replace :key="warehouse.id" by :key="'warehouse' + warehouse.id"

(because you can't have the same components (l-marker) within the same parent with the same keys)