Iphone 11 Notification Delayed in some Social Applications

Recently i got some issues using social applications. Apps like whatsapp, telegram, etc sometimes doesn’t recieve any notifications (can’t recieve any messages) if the apps not opened. I already tried to do network reset, the problem still there. Already tried to use Wi-Fi and Cellular Data, but the result is the same.

Is this problem related to my hardware, or the operational system? Or maybe the apps? I use iOS 14.2.

Is there any other options to fix this problem? Other than network reset or hard reset?