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As the lock screen and notification screen are joined on iOS 11, once you see the notification it will hide so you can clearly see your lock screen without all the stuff you were noticed still pollute the desk. If you still wanna see your notifications just swipe your finger up, and it will display a history of notifications you haven't dismissed.
Extra tip: make sure all your relevant apps has access to notifications, and they can "Show in history" at "Settings> notifications> Notification style" select the apps you wanna be notificated, and then look if under "Alerts" the switch "Show in history" is turned on.
Hope it helps
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