This would make sense as https://www.npmjs.com/package/mini-css-extract-plugin was released 15h ago, and has a breaking change in its packaging that seems to affect a lot of people webpack-contrib/mini-css-extract-plugin#896

As a temporary workaround, add

"resolutions": {
    "mini-css-extract-plugin": "~2.4.5"
  }

to your project

I have the same problem and extract-css its my problem:

/* config.plugin('extract-css') */
    {
      args: [
        {
          filename: 'css/[name].[contenthash:8].css',
          chunkFilename: 'css/[name].[contenthash:8].css'
        }
      ]
    }

I try this adding this to packaje.json with npm:

"overrides": {
    "mini-css-extract-plugin": "~2.4.5"
}

But without result. Any ideas?

npm overrides seems to work a little differently to yarn resolutions - do you have a direct dependency on mini-css-extract-plugin in your package.json?

Also, the problem was fixed in the plugin, so the latest version should be fine now.

I solved it adding mini-css-extract-plugin@~2.4.5 to devDependencies