Push Notifications are not received when sent to many users at once

Hello, I have an application available in Android market, and running on some IOS devices, it will be available in Apple App Store soon.
Whenever I send push notification to all users at once ( around 500-600 users so far ) , status of the push is marked as “enqueued” however it is not received by clients.
But If I try to send a push notification to limited number of users, say 3-5 they immediately receive the notification.
I tried to limit push to 5 users at a time, instead of making 1 request with 500 users I tried making 100 requests to ionic push services with 5 users but it doesn’t work.
I am using same piece of code and same configuration when I send push notification to limited number of users, and it works; so I don’t think it is a configuration problem.
Any ideas about what I am missing or doing wrong ?

@Mephalay this problem is not related to amount of tokens to send notifications, and yes, the token itself be valid or not. For some reason (I’m still in search), some tokens (iOS / Android) become invalid and push not sent to all the desired token group. I’m going through this problem and you can track the progress of it here: https://github.com/driftyco/ionic-platform-web-client/issues/141#issuecomment-242768242