It’s possible that you accidentally activated the Notification Manager feature in dfndr security which turned off your notification alerts.

To disable this feature and receive all notifications again, please follow these steps:

1. Open the dfndr security app and tap on Tools;
2. Scroll down to Notification Manager (click from a smartphone);
3. Tap on Hidden
4. If you want to unblock all notifications, tap on the button next to “Make all apps alerts visible” and select Yes.
   or
   If you want to unblock a specific notification, just tap on the Visible button next to the app from which you want to receive the notification.

Notification Manager has now been disabled and you will receive notifications for all apps on your device again.