If you are in Do No Disturb mode but still receive notification errors from specific apps then you will need to go into the settings to disallow notifications for that specific app.
- From the Home screen, tap Settings.
- Scroll to and then tap Notifications.
- Select the app you’re having notification errors with.
- Make sure that the switch next to Allow Notifications is turned OFF.
For more troubleshooting for iPhone 11 notifications errors visit here.