sounds a little messy. Seems to be trying to use cdn for online cdn but not locally?
https://www.jianshu.com/p/9d6...
this may help you

your config.externals configuration is not added to the returned result, is it?

    configureWebpack: config => {
        //and
        let pluginsPro = [
            new vConsolePlugin({
                filter: [], 
                enable: true
            }),    
            new CompressionPlugin({ 
                filename: '[path].gz[query]',
                algorithm: 'gzip',
                test: new RegExp('\\.(' + ['js', 'css'].join('|') + ')$', ),
                threshold: 8192,
                minRatio: 0.8,
            })    
            new BundleAnalyzerPlugin(),
        ];
        //
        let pluginsDev = [
            new vConsolePlugin({
                filter: [], 
                enable: true
            }),        
        ];
        if(isPRO) { 
            config.plugins = [...config.plugins, ...pluginsPro];
        } else {
            config.plugins = [...config.plugins, ...pluginsDev];
        }
    },

isPRO is a variable that determines the environment

after checking the information for a day, I finally solved it. Post a solution for partners with the same needs to use

reference to third-party libraries in 1.main.js

//main.js
import Cesium from 'cesium/Cesium'//

2.vue.config.js (without creating a new one in the root directory), fill in the following code

configureWebpack: config => {
    let settings = {};
    if (process.env.NODE_ENV === 'production') {
      settings = {
        plugins: [
          new webpack.DefinePlugin({
            'CESIUM_BASE_URL': JSON.stringify('static')
          }),
          new CopyWebpackPlugin([{
            from: path.join(cesiumSource, cesiumWorkers),
            to: 'static/Workers'
          }]),
          new CopyWebpackPlugin([{
            from: path.join(cesiumSource, 'Assets'),
            to: 'static/Assets'
          }]),
          new CopyWebpackPlugin([{
            from: path.join(cesiumSource, 'Widgets'),
            to: 'static/Widgets'
          }])
        ],
        externals: {
        //cesium/Cesium  import Cesium from 'cesium/Cesium'
        //'cesium/Cesium'CesiumCesium
          "cesium/Cesium": "Cesium" 
        }
      }

    } else {
      settings = {
        plugins: [
          new webpack.DefinePlugin({
            'CESIUM_BASE_URL': JSON.stringify('')
          }),
          new CopyWebpackPlugin([{
            from: path.join(cesiumSource, cesiumWorkers),
            to: 'Workers'
          }]),
          new CopyWebpackPlugin([{
            from: path.join(cesiumSource, 'Assets'),
            to: 'Assets'
          }]),
          new CopyWebpackPlugin([{
            from: path.join(cesiumSource, 'Widgets'),
            to: 'Widgets'
          }]),
        ]
      }
    }
    return settings
  }

ps: I set alias in the project. If you use this place, you can modify it according to your needs

chainWebpack: config => {
    config
      .node.set('fs', 'empty').end()
      .resolve.alias.set('cesium', path.resolve(__dirname, cesiumSource)).end().end()
  }

then build directly.
reference link: https://blog.csdn.net/qq_1524...