If you have installed any battery-saving app on your device then you can uninstall it and check for the notifications. Similar to Android, you can check for battery-saving apps. Solution for iOS user for WhatsApp Notifications Then tap on WhatsApp and make sure that “restrict background data” is off, if not then do it and now check for notifications. Turn off restrict background data: Open device Settings, look for Data Usage. For this, you need to check the “restrict background data” in your device settings. It might happen that even after having a good internet connection your WhatsApp notifications are delayed. READ ALSO: Know If WhatsApp Contact Is Online With This WhatsApp Online Notifier Delay in receiving WhatsApp Notification messages
Some of the users report that they get notifications when they are connected to the WiFi. It might be the issue with your mobile network.