Finally heard back from Whatsapp but the response is pretty much what happened already been said on this forum. Here it is anyway:
“Hi,
Thanks for your message.
When you receive a message or a call in WhatsApp, but are not online, WhatsApp will automatically send a message to the Apple Push Notification Service (APNS). This allows an alert to be displayed, even when WhatsApp is closed or when your phone's display is off. Most often, all that is needed to resolve WhatsApp notification issues is to ensure that all notification settings are enabled. Review the following FAQ pages for troubleshooting steps:
The message WhatsApp sends to APNS typically takes only a few milliseconds. Once the message is sent to APNS, any delays or failure to deliver the message as a push notification to your device are usually caused by issues with your phone or with network connection. Currently, all of our systems are operating normally.
To ensure push notifications are working correctly on iOS 11, please don't force close WhatsApp. Frequently force closing apps can cause data loss and excessive battery usage.
Note: Force closing is when you double tap the home button and swipe up on an app.
If you are using iOS 7 or later, and are confident that you have all push notification settings enabled in WhatsApp and in your iPhone's Notifications settings, then there is likely an issue with your phone that WhatsApp cannot resolve. In this case, the following steps are recommended:
Backup your entire phone to iCloud (http://support.apple.com/kb/ht1766).
- Continue setting up your phone as a new device (don't restore from the iCloud backup).
- Install WhatsApp and verify that push notifications are working correctly (have someone send a test message while your phone's display is turned off).
- Erase all content and settings and restore from the iCloud backup.
Regards, Tom WhatsApp Support Team”