In the current implementation we are only receiving notifications when the app is in foreground. In background, the code won't receive any notifications until users click on the notification.
This is mostly not a problem because users see the notifications at the OS level anyways, and once they click on it everything works as expected. However, some situations are not ideal. For example, the notification count in the icon badge is not updated as reported in the forum.
One solution would be to use content-available property, but this has been tested before and it wasn't working as expected in iOS.