When you set up notifications for an app, you can set them as 'silent' notifications, which means that they'll still be in the notification area (hence that 'Silent Notifications' area...the 'X' is to clear all those below). They will not make sounds, vibrations, nor pop-ups, but will still show the notification (as opposed to setting it up as 'Do not allow notifications' where the notification is completely blocked).
If all your notifications are there, you might have Do not Disturb options active or, somehow, all your app notifications got changed to Silent Notifications.
You should be able to change that if you long-press on any notification and see if it's set to 'Alert' or 'Silent'. Furthermore you can go to the Details option to further customize the notification.