See cross-posted question on Stack Overflow: http://stackoverflow.com/questions/36649838/push-notification-not-getting-delivered-via-service-workers

For users clearing cookies in Chrome our new Important Sites system that Dru is working on should help, but I don't think there's anything we can practically do about 3rd party apps clearing push subscriptions.

In case anyone is wondering about how the cross-domain push plan will work with Site Engagement I don't think this should be an issue since push that trigger notifications shouldn't require any engagement quota, although in general being on the same origin will help with clearing previously sent notifications and advanced push use cases.

HI
I also wanted to know is there is there anything in works that gives info on what happened to push notifications ? 

GCM has it in play console where exact journey of a push is given. 
We are getting message ids for most of the active subscribers but when we are not getting impressions in our analytics saying it reached the device. 

Can a system be built which explains what happened to push notification is given. 
Also can information be passed if there any cache clearing or anything that took away the device token of that device ? That would be really helpful as then we can understand what is causing that the device tokens to go away. 

Right now our stats are 400K active subscribers for which we get valid message ids and only 50K impressions for them even when the push expiry is 10 days. 

> we do not have a direct way to get them back even if they come to our website

If the user clicks Clear Data for Chrome in Android Settings, or uses an app with the same effect, then it's as if Chrome has been completely uninstalled and reinstalled, and there is nothing Chrome can do about that. Handle it the same way you would handle the user switching to a new device. Note that the Google Cloud Messaging server won't know that Chrome's app data was cleared, so the next message you send to the device may appear to succeed (GCM will return a message id, rather than a NotRegistered error), but when Chrome receives the message for the no-longer-valid registration it will unsubscribe from GCM, so subsequent messages sent to GCM should return NotRegistered as expected.

If instead the user clicks Clear Cache for Chrome in Android Settings, or uses an app with the same effect, then Service Workers and push subscriptions seem to be unaffected.

If instead the user clicks Chrome Settings > Privacy > Clear browsing data (and ticks at least the Cookies and site data box) then this will clear your Service Worker, but will not clear permissions previously granted by the user. So next time the user visits your main site, it should be possible to embed an https://notify.buyhatke.com/ iframe which re-registers the Service Worker and re-subscribes to push without re-prompting.

> anything in works that gives info on what happened to push notifications?

See https://bugs.chromium.org/p/chromium/issues/detail?id=606806#c7 for monitoring what happens to push notifications.

When does Chrome receive the no longer valid registration message and where does it receive it ? Can as a developer we get an access to it where we pass on that info to our backend. 
We still receive about 50K odd impressions only with 540K active users subscribed for whom we get message ids.  
This link https://docs.google.com/spreadsheets/d/1sXBPgzQfAa0gboTJvAF7Bso_IrhYIzgU-g2OiujhHkA/edit#gid=0 gives some data on the push notifications we had sent. The active subscribers we had then and how many impressions we received, CTR and other details. 

The iframe part we have done. And we would be implementing XMPP for getting more insights onto push.