offline service worker not working properly in google dev tools

I have been leaning to make PWA and I have notice google dev tools are not properly simulating offline feature of service worker.

I am talking about this feature showed in image.
I am using

package.json

"devDependencies": {
    "http-server": "^0.9.0"
  }

for localhost web server

SW.js file

var CACHE_STATIC_NAME = 'static-v10';
var CACHE_DYNAMIC_NAME = 'dynamic-v2';

self.addEventListener('install', function(event) {
  console.log('[Service Worker] Installing Service Worker ...', event);
  event.waitUntil(
    caches.open(CACHE_STATIC_NAME)
      .then(function(cache) {
        console.log('[Service Worker] Precaching App Shell');
        cache.addAll([
          '/',
          '/index.html',
          '/offline.html',
          '/src/js/app.js',
          '/src/js/feed.js',
          '/src/js/promise.js',
          '/src/js/fetch.js',
          '/src/js/material.min.js',
          '/src/css/app.css',
          '/src/css/feed.css',
          '/src/images/main-image.jpg',
          'https://fonts.googleapis.com/css?family=Roboto:400,700',
          'https://fonts.googleapis.com/icon?family=Material+Icons',
          'https://cdnjs.cloudflare.com/ajax/libs/material-design-lite/1.3.0/material.indigo-pink.min.css'
        ]);
      })
  )
});

self.addEventListener('activate', function(event) {
  console.log('[Service Worker] Activating Service Worker ....', event);
  event.waitUntil(
    caches.keys()
      .then(function(keyList) {
        return Promise.all(keyList.map(function(key) {
          if (key !== CACHE_STATIC_NAME && key !== CACHE_DYNAMIC_NAME) {
            console.log('[Service Worker] Removing old cache.', key);
            return caches.delete(key);
          }
        }));
      })
  );
  return self.clients.claim();
});

self.addEventListener('fetch', function(event) {
  event.respondWith(
    caches.match(event.request)
      .then(function(response) {
        if (response) {
          return response;
        } else {
          return fetch(event.request)
            .then(function(res) {
              return caches.open(CACHE_DYNAMIC_NAME)
                .then(function(cache) {
                  cache.put(event.request.url, res.clone());
                  return res;
                })
            })
            .catch(function(err) {
              return caches.open(CACHE_STATIC_NAME)
                .then(function(cache) {
                  return cache.match('/offline.html');
                });
            });
        }
      })
  );
});

this is service worker file. I am trying to show offline.html page if any page

let me know if you need any thing more regarding project I am working with