Gulp browserify task stuck

Question

Gulp terminal seems to get stucked after browserify-ing my main.js. Below is my gulpfile.babel.js

'use strict';

import gulp from 'gulp';
import gulpLoadPlugins from 'gulp-load-plugins';
import browserSyncLib from 'browser-sync';
import pjson from './package.json';
import minimist from 'minimist';
import glob from 'glob';

// Load all gulp plugins based on their names
// EX: gulp-copy -> copy
const plugins = gulpLoadPlugins();

const defaultNotification = function(err) {
  return {
    subtitle: err.plugin,
    message: err.message,
    sound: 'Funk',
    onLast: true,
  };
};

let config = Object.assign({}, pjson.config, defaultNotification);

let args = minimist(process.argv.slice(2));
let dirs = config.directories;
let taskTarget = args.production ? dirs.destination : dirs.temporary;

// Create a new browserSync instance
let browserSync = browserSyncLib.create();

// This will grab all js in the `gulp` directory
// in order to load all gulp tasks
glob.sync('./gulp/**/*.js').filter(function(file) {
  return (/\.(js)$/i).test(file);
}).map(function(file) {
  require(file)(gulp, plugins, args, config, taskTarget, browserSync);
});

// Default task
gulp.task('default', ['clean'], () => {
  gulp.start('build');
});

// Build production-ready code
gulp.task('build', [
  'browserify'
]);

// Testing
gulp.task('test', ['eslint']);

This is my browserify.js

'use strict';

import path from 'path';
import glob from 'glob';
import browserify from 'browserify';
import watchify from 'watchify';
import envify from 'envify';
import babelify from 'babelify';
import _ from 'lodash';
import vsource from 'vinyl-source-stream';
import buffer from 'vinyl-buffer';
import gulpif from 'gulp-if';

export default function(gulp, plugins, args, config, taskTarget, browserSync) {
  let dirs = config.directories;
  let entries = config.entries;

  let browserifyTask = (files) => {
    return files.map((entry) => {
      let dest = path.resolve(taskTarget);

      // Options
      let customOpts = {
        entries: [entry],
        debug: true,
        transform: [
          babelify, // Enable ES6 features
          envify // Sets NODE_ENV for better optimization of npm packages
        ],
        paths: ['./node_modules','./src/_modules/', './src/Cwp/assets/PTM/scripts/', './src/_Cwp/assets/PTM/scripts/']
      };

      let bundler = browserify(customOpts);

      if (!args.production) {
        // Setup Watchify for faster builds
        let opts = _.assign({}, watchify.args, customOpts);
        bundler = watchify(browserify(opts));
      }

      let rebundle = function() {
        let startTime = new Date().getTime();
        bundler.bundle()
          .on('error', function(err) {
            plugins.util.log(
              plugins.util.colors.red('Browserify compile error:'),
              '\n',
              err.stack,
              '\n'
            );
            this.emit('end');
          })
          .on('error', plugins.notify.onError(config.defaultNotification))
          .pipe(vsource(entry))
          .pipe(buffer())
          .pipe(plugins.sourcemaps.init({loadMaps: true}))
            .pipe(gulpif(args.production, plugins.minify()))
            .on('error', plugins.notify.onError(config.defaultNotification))
          .pipe(plugins.rename(function(filepath) {
            // Remove 'source' directory as well as prefixed folder underscores
            // Ex: 'src/_scripts' --> '/scripts'
            filepath.dirname = filepath.dirname.replace(dirs.source, '').replace('_', '');
          }))
          .pipe(plugins.sourcemaps.write('./'))
          .pipe(gulp.dest(dest))
          // Show which file was bundled and how long it took
          .on('end', function() {
            let time = (new Date().getTime() - startTime) / 1000;
            console.log(
              plugins.util.colors.cyan(entry)
              + ' was browserified: '
              + plugins.util.colors.magenta(time + 's'));
            return browserSync.reload('*.js');
          });
      };

      if (!args.production) {
        bundler.on('update', rebundle); // on any dep update, runs the bundler
        bundler.on('log', plugins.util.log); // output build logs to terminal
      }
      return rebundle();
    });
  };

  // Browserify Task
  gulp.task('browserify', (done) => {
    return glob('./' + path.join(dirs.source, dirs.scripts, entries.js), function(err, files) {
      if (err) {
        done(err);
      }

      return browserifyTask(files);
    });
  });
}

When I execute gulp build in my terminal, below output is:

C:\Users\Chan\Downloads\Frontend\Frontend>gulp build
[23:25:23] Requiring external module babel-register
[23:25:25] Using gulpfile ~\Downloads\Frontend\Frontend\gulpfile.babel.js
[23:25:25] Starting 'browserify'...
[23:25:26] 842639 bytes written (1.21 seconds)
[23:25:27] 831961 bytes written (1.55 seconds)
./src/_Cwp/assets/PTM/scripts/main-contribute-form-iframe.js was browserified: 1.751s
./src/_Cwp/assets/PTM/scripts/main-vip-tree-iframe.js was browserified: 1.607s
[23:25:27] 1445674 bytes written (1.76 seconds)
./src/_Cwp/assets/PTM/scripts/main-plot-tree-iframe.js was browserified: 1.853s
[23:25:31] 7046431 bytes written (5.32 seconds)
./src/_Cwp/assets/PTM/scripts/main.js was browserified: 5.589s

The terminal looks stucked. what seems to be the problem here?