Migrated to VM - had continuous delays on Whatapp and some others (unless connected to Wifi, in which case it worked fine). Replacement sim card made no difference and moved to a new handset, same issue.
Migrated away to Vodafone - Whatsapp worked properly again.
This is WhatsApp messages and emails are not received and no notification is sent until the app has been opened. This only happens on 4g when using WiFi there is no issue. I have checked changed settings swapped sim cards to no avail. I have contacted WhatsApp and they have advised that this a network issue as the problem is only on 4g.