Sometimes the phone just does not push notifications.
I saw this especially on whatsapp and sometimes on instagram.
I don't see a pattern for this. Sometimes I get them, sometimes I get them in bulk with I open the application.
Also, when I receive them, they do not show an icon or something in the lock screen, even if in the settings, it's set to wake up screen .
The only application that shows is the phone (e.g. missed call) or messages (new sms message), other applications don't do this.
Best answer by IDM88