Are you getting any error messages when trying to use the biometrics on your Note 9?
Does the phone itself power off when you try to use the biometrics? I would recommend removing the biometrics and reapplying them within Biometrics and Security in your settings. You can do so by following these steps.
Navigate to Settings > Biometrics and Security
Tap on either Face recognition, Irises, or Fingerprints. Whichever biometric security you have set up.
(If a pattern password or pin password is set up on the device, you phone will require this to view the biometrics.)
Tap on the biometric registered and you should see in the top right a remove option. Select this for each biometric to remove them.
Once removed, add the biometrics you would like and test to see if you are experiencing the same symptoms.
Let me know if this helped!