WhatsApp delayed messages and calls

Hey Apple Team,

I am facing a pretty big issue in my iPhone 13 iOS 15. My some of the WhatsApp messages are delayed and even sometimes WhatsApp call does not appear when i am not using WhatsApp. When i open the app suddenly missed calls pop up. I have seen a lot of suggestions regarding this issue tried every single step but nothing worked. Checked background app refresh, checked notifications settings, screen time is also on, i have a good internet connection, WhatsApp is also up to date and even i am using latest iOS 15.4. I have reseted all the settings still nothing worked. Restarted my iPhone. But nothing seems to be working. I have been doing a lot of research about solutions and tried everything nothing worked. I think there is a problem in iOS. Please suggest any good solutions regarding this or solve this issue in next iOS update.

Thank you