nunjucks.config.js

/**
 * Generate HTML files from Nunjucks
 */

const mix = require('laravel-mix'),
      path = require('path'),
      fs = require('fs'),
      paths = require('./paths'),
      HTMLWebpackPlugin = require('html-webpack-plugin');

var templateParameters = require('./data.json');

let env = 'development';
if (mix.inProduction()) {
    env = 'production'
}

const directories = []
function walkDir(dir, parent = '') {
    var files = fs.readdirSync(dir);
    for(var x in files){
        var next = path.join(dir,files[x]);
        if(fs.lstatSync(next).isDirectory()==true){
            walkDir(next, parent+'/'+files[x]);
        } else {
            directories.push([path.parse(files[x]).name, (parent+'/').slice(1)]);
        }
    }
    return directories
}

const pages = {
    generatePages: function generatePages(pagesPath) {
        return walkDir(pagesPath).map(
            name =>
                new HTMLWebpackPlugin({
                    template: `${pagesPath}/${name[1]}${name[0]}.njk`,
                    filename: paths.pages.base + `/${name[1]}${name[0]}.html`,
                    templateParameters: templateParameters
                })
        );
    }
};

module.exports = pages;

paths.json

{
    "base": {
        "dir": "./pages",
        "node": "node_modules",
        "start": "index.html"
    },
    "src": {
        "base": "./src",
        "scss": "./src/scss",
        "templates":  "./src/templates",
        "js": "./src/js",
        "fonts": "./src/fonts",
        "images": "./src/images"
    },
    "pages": {
        "base": "./pages",
        "assets": "./pages/assets",
        "layouts": "./pages/layouts",
        "block": "./pages/blocks",
        "js": "./pages/assets/js",
        "css": "./pages/assets/css",
        "fonts": "./pages/assets/fonts",
        "images": "./pages/assets/images",
        "vendor": "./pages/assets/vendor"
    },
    "dist": {
        "base": "./dist",
        "css": "./dist/assets/css",
        "js": "./dist/assets/js",
        "pages": "./dist/pages",
        "layouts": "./dist/pages/layouts",
        "blocks": "./dist/pages/blocks",
        "vendor": "./dist/assets/vendor",
        "fonts": "./dist/assets/fonts",
        "images": "./dist/assets/images"
    }
}

webpack.mix.js

const paths = require('./paths'),
      mix = require('laravel-mix'),
      RemoveWebpackPlugin = require('remove-webpack-plugin'),
      nunjucksConfig = require('./nunjucks.config'),
      path = require('path'),
      WebpackOnBuildPlugin = require('on-build-webpack');

  mix.webpackConfig({
      module: {
          rules: [
            {
              test: /\.njk$/,
                  use: [
                      {
                          loader: 'simple-nunjucks-loader'
                      }
                  ]
              }
          ]
      },
      plugins: [
          ...nunjucksConfig.generatePages(path.resolve(__dirname, paths.src.templates)),
      ]
  })

I think it's relate to how webpack config works. Webpack trying to use obsolete config.

I'm afraid webpack doesn't reload config, when entry point files changes. There definitely should be some solution.