Chrome Push Notification: This site has been updated in the background

I was expriencing the same issue but after a long research I got to know that this is because delay happen between PUSH event and self.registration.showNotification(). I only missed return keyword before self.registration.showNotification()

So you need to implement following code structure to get notification:

var APILINK = "https://xxxx.com"; self.addEventListener('push', function(event) {      event.waitUntil(          fetch(APILINK).then(function(response) {        return response.json().then(function(data) {                  console.log(data);                  var title = data.title;                  var body = data.message;                  var icon = data.image;                  var tag = 'temp-tag';                  var urlOpen = data.URL;                return  self.registration.showNotification(title, {                      body: body,                      icon: icon,                      tag: tag                  })              });          })      );  });

I've run into this issue in the past. In my experience the cause is generally one of three issues:

1. You're not showing a notification in response to the pushmessage. Every time you receive a push message on the device, whenyou finish handling the event a notification must be left visible onthe device. This is due to subscribing with the userVisibleOnly:true option (although note this is not optional, and not setting itwill cause the subscription to fail.
2. You're not calling event.waitUntil() in response to handling the event. A promise should be passed into this function to indicate to the browser that it should wait for the promise to resolve before checking whether a notification is left showing.
3. For some reason you're resolving the promise passed to event.waitUntil before a notification has been shown. Note that self.registration.showNotification is a promise and async so you should be sure it has resolved before the promise passed to event.waitUntil resolves.

Generally as soon as you receive a push message from GCM (Google Cloud Messaging) you have to show a push notification in the browser. This is mentioned on the 3rd point in here:

https://developers.google.com/web/updates/2015/03/push-notificatons-on-the-open-web#what-are-the-limitations-of-push-messaging-in-chrome-42

So it might happen that somehow you are skipping the push notification though you got a push message from GCM and you are getting a push notification with some default message like "This site has been updated in the background".