UserAgent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/70.0.3538.110 Safari/537.36

Steps to reproduce the problem:
1. Collect subscribers for Web Push Notification Service 
2. Shoot a message
3. Many of the subscribers will be unsubscribed with error NotRegistered

What is the expected behavior?
The subscribers cannot become NotRegistered on the first message shot. 

Unsubscription is getting so high for even the first time subscribers, who had never received any message. That means that if the website started web push notification service, and visitors subscribed to that website , within few hours close to say 12 hours a thousand unsubscribed reports from web push on the first message sent after 12 hours. 

Points to consider is , We are taking care of updating and monitoring the new token as soon it is changed and sending out the next messages on those new token only, but in the above explained case this does not come into scenario as it was a first ever message of that website to its subscribers and google said that 1020 are unsubscribers out of 17,000

In a time duration of 12 hours ago, we sent the first message, to our wonder we got the following stats:

Total Subscription : 17,000

Total UNSubscription with Error NotRegistered is 1020

What went wrong?
This much of unsubscribers are not possible. 

Did this work before? N/A 

Chrome version: 70.0.3538.110  Channel: n/a
OS Version: 10.0
Flash Version: 

Attaching the list of unsubscribers for your review.

Sample payload request and response including the headers

REQUEST
POST /fcm/send HTTP/1.1
Host: fcm.googleapis.com
Authorization: key=AAAAT-vcCPU:APA91bFaX5qCg-xrd1p88fAiSIClIzLwtLVwMH7R0kWPopY3xTg3P5PuTEgJa7zRQEbN9SOJPbwxXkQM82tYFAAY_vsA0oRunPEUwA_gVm3871rhVABZ0tCCVUQzfGZcA6gE6t6m6JqVZJvNyX9e2E-dfz-v0uRC4A
Content-Type: application/json
Cache-Control: no-cache
Postman-Token: 59e245b0-4cad-8762-f966-4d1acbf097a8

{
  "registration_ids": [
    "fAcOnqtNygg:APA91bE_HRkcyL0Hu9fqwmrisvhj6YZ5PkAUmUU40z4U36K30LQDbGYWmrIbCGQ6FmderLPJruFK22RbEHCv1fEpRypBSI8eOjwIfOe8hRQ8qualGyZLsDAAY96FxCmkWiY_2kf9a3Jg"
  ]
}

RESPONSE
{
    "multicast_id": 8971516683071751207,
    "success": 0,
    "failure": 1,
    "canonical_ids": 0,
    "results": [
        {
            "error": "NotRegistered"
        }
    ]
}