vue-loader was used without the corresponding plugin. Make sure to include VueLoaderPlugin in your w ebpack config.

Vue Loader v15 现在需要配合一个 webpack 插件 VueLoaderPlugin 才能正确使用

// webpack.config.js
const VueLoaderPlugin = require('vue-loader/lib/plugin')

module.exports = {
  // ...
  plugins: [
    new VueLoaderPlugin()
  ]
}

官方文档：https://vue-loader.vuejs.org/zh/migrating.html