I’m sorry the article did not provide much help!
let’s see.... what app is this specifically?
is it just one app or all of them doing this to you?
if it’s one app, try going through that apps settings. Either within the app and find something related to notifications and see if possibly there’s a bypass to the system setting for notification
if not, another place for specific app settings is:
settings > scroll to very bottom and find the app your talking about and make sure notifications is correct for it.
make sure too, do not disturb is off. Can be enabled and disabled via control center. iPhone 8, swipe up from bottom of screen and press the moon
https://support.apple.com/en-us/HT204321
if you have an Apple Watch too make sure of that. Swipe up on screen and toggle moon on/off
found couple more things:
- try and see if it’s your WiFi connection causing the issue.
- if connected to WiFi, turn WiFi off, and test by emailing yourself or texting yourself if either of those apps are troubling you. If notification appears, whoever configured your modem/router’s firewall has got it set to custom and possibly has the necessary IP and ports for notifications blocked (very technical) https://support.apple.com/en-us/HT203609
if issue continues, try restarting the device https://support.apple.com/en-us/HT201559
found this too.
https://support.apple.com/guide/iphone/change-notification-settings-iph7c3d96bab/ios
this goes in extreme detail and may be useful https://developer.apple.com/library/archive/documentation/NetworkingInternet/Conceptual/RemoteNotificationsPG/APNSOverview.html
hope this helps!