gulp watch with elixir 6 - stream.js throws error

Level 4
I get this as well. Randomly started happening after adding versioning one day, even tho versioning was working great before. Were you able to solve it?
My gulp file:
const elixir = require('laravel-elixir');

require('laravel-elixir-vue');

/*
 |--------------------------------------------------------------------------
 | Elixir Asset Management
 |--------------------------------------------------------------------------
 |
 | Elixir provides a clean, fluent API for defining some basic Gulp tasks
 | for your Laravel application. By default, we are compiling the Sass
 | file for our application, as well as publishing vendor resources.
 |
 */

elixir(mix => {
    Elixir.webpack.mergeConfig({
        progress: false,
        devtool: 'source-map',
        module: {
            loaders: [
                {
                    test: /\.jsx$/,
                    loader: 'babel'
                },
                {
                    test: /\.js$/,
                    loader: 'babel',
                    exclude: /node_modules/
                },
            ]
        }
    });

    mix.sass('app.scss')
        .webpack('app.js')
        .webpack('backend.js')
        .version(['css/app.css', 'js/app.js', 'js/backend.js'])
        .copy('node_modules/bootstrap-tokenfield/dist/bootstrap-tokenfield.min.js', 'public/js/bootstrap-tokenfield.min.js')
        .copy('node_modules/bootstrap-tokenfield/dist/css/bootstrap-tokenfield.min.css', 'public/css/bootstrap-tokenfield.min.css')
        .copy('node_modules/bootstrap-tokenfield/dist/css/tokenfield-typeahead.min.css', 'public/css/tokenfield-typeahead.min.css')
        .copy('node_modules/sweetalert/dist/sweetalert.min.js', 'public/js/sweetalert.min.js')
        .copy('node_modules/sweetalert/dist/sweetalert.css', 'public/css/sweetalert.css')
        .copy('node_modules/jquery-slimscroll/jquery.slimscroll.min.js', 'public/js/jquery.slimscroll.min.js')
        .copy('node_modules/bootstrap-switch/dist/js/bootstrap-switch.min.js', 'public/js/bootstrap-switch.min.js')
        .copy('node_modules/bootstrap-switch/dist/css/bootstrap3/bootstrap-switch.min.css', 'public/css/bootstrap-switch.min.css')
        .copy('node_modules/wowjs/dist/wow.min.js', 'public/js/wow.min.js')
        .copy('node_modules/ladda/dist/spin.min.js', 'public/js/spin.min.js')
        .copy('node_modules/ladda/dist/ladda.min.js', 'public/js/ladda.min.js')
        .copy('node_modules/ladda/dist/ladda.min.js', 'public/js/ladda.jquery.min.js')
        .copy('node_modules/ladda/dist/ladda-themeless.min.css', 'public/css/ladda-themeless.min.css')
        .copy('node_modules/pace-js/pace.min.js', 'public/js/pace.min.js')
        .copy('node_modules/metismenu/dist/metisMenu.min.js', 'public/js/metisMenu.min.js')
        .copy('node_modules/metismenu/dist/metisMenu.min.css', 'public/css/metisMenu.min.css');
});