iPhone notifications not working on iOS 14.4

Hello,

This has been a recurring issue since I've had this phone (iPhone XS Max) two years ago, and present in every single iOS version available. Push notifications work fine for months, but then every single app stops having notifications at the same time. It's not just Messages, but also Gmail, Telegram, WhatsApp, Discord, etc. I've contacted support a couple of times and so far the only two solutions that temporarily solve the issue are re-installing every affected app, or reseting the entire phone to a factory state (restoring from a back-up won't work) and then re-downloading everything. None of the other tricks out there appear to work (bluetooth, airplane mode, watch notifications, do not disturb, etc.). I've seen a few threads trying to address the issue by mentioning that it might be related to some notification settings, but I can assure that this isn't the case.

The issue happens almost randomly and it affects all of the applications at the same time. Out of the numerous times that it has happened, in one instance it started occurring when the iPhone's memory was almost full; and in the latest case the moment I activated "Do not disturb".

Applications only receive notifications badges for a very brief period of time after you exit them (not close), about 1-2 seconds. After that, they "freeze", and neither push notifications nor badges appear.

I was wondering if anyone has had this kind of issue and if there are any better workarounds rather than having to re-install every application.

Thank you.

[Re-Titled by Moderator]