Push notification systems allow applications installed in mobile devices to send alerts when we receive messages, an email, someone interacts with us on social networks, etc. In the case of Apple, the Push notification system is designed to deliver a percentage of all alerts sent by a developer to its users, but Apple acknowledges that it cannot guarantee that all notifications will be sent to iDevices.
With that in mind, you've probably come across at least one time when applications installed on your iDevices no longer receive push notifications, and you've probably wondered why. The reality is that you will not receive a simple and clear explanation, but there is a solution for this problem and it is as simple as possible, in most cases, the solution is still temporary.
How do I troubleshoot applications that no longer send notifications?
If an iPhone or iPad application stops sending notifications, simply deleting it and reinstalling it from the App Store can quickly fix the problem, in most cases this being the only procedure required. If you still can't fix everything like this, then you will need to delete the application to reset the network settings via Settings> General> Reset> Reset Network Settings, this procedure including deleting saved passwords for WiFi networks.
If this process does not resolve the issue, then either contact the application developer or perform a restore without restoring an iOS backup.