Are there any properties in an app configuration (plists and such) that could cause push notifications not to show in the notification center?

I am posting this again with more clarity. https://apple.stackexchange.com/questions/377573/user-reporting-that-push-notification-doesnt-always-show-in-the-notification-ce?noredirect=1#comment509275_377573 I have an app. My client is reporting that push notifications from the app DO NOT go into the notification center. To me, that sounds like an OS settings issue, as mentioned by the commenter on the other issue. However I want to get authoritative information on whether there's any way - any possible way, that this is due to some sort of misconfiguration of plist files or something else in the actual development of the app. I've googled for this, I've searched for this, and I haven't found anything, which is why I am asking here. So my question is - is there any type of misconfiguration, in the actual build of the app (which I have developed) that could lead to push notifications not appearing in the notification center? Note, they DO appear at the top of the user's screen, and I personally see them in my notification center, as do most users to my knowledge. The user in question is on iOS 13, on an iPhone 11. Personally, I think it's an OS settings issue, but they're a non-technical user and I am trying to troubleshoot if it could **possibly** be something on my end.