Hi, Make sure to fully cover the fingerprint sensor with your finger to prevent strong light from entering the fingerprint sensor.
For more information, check the below link.
If you mean a glass screen protector, most will interfere with the finger print scanner, especially those that don't use edge to edge adhesives.
I use Whitestone Dome tempered glass screen protectors & there's zero issues with the FP scanner.
Remove the screen protector & you shouldn't have any problems registering your finger prints.
Hi, If you use a screen cover with a bumped or dotted pattern including dome glass, toughened glass cover, or thick protective films in addition to silicone cover. And you should make sure to use the central fingerprint parts evenly when you register or scan fingerprint so that all portions of the fingerprint, including the center and corners have been fully scanned.
If you still have similar problems while registering or scanning your fingerprints, please visit to the Authorized Samsung Service Center with the device and get proper actions.