IOS users have a big problem with WhatsApp notifications for last ten days. Notifications are eir coming too late or messages don't drop to main screen without opening app. The issue of frequent posts in first transition to IOS 11 has been resolved. However, problem of notification has become much more annoying and goes on.
According to Webtekno for this issue, you can follow steps below to reach a solution. By implementing a method such as resetting application's notification settings, notifications are returning to its former state. At least it's not a problem for now.
Go to Settings section of app. Just under Chats, click Notifications.
Click Reset Notification Settings at top of probe. nn