Please perform the following steps to resolve the issue:
1- Kindly delete all registered face lock and re-register the face lock.
2- Ensure that you are in a well-lit area and that the camera lens is clean while registering.
3- Ensure your image is not blurry for better match results.
For further assistance, register your concern in Samsung members app(Open Samsung members app>click on “+“icon>send feedback>Error report/ Ask Questions).
Team Samsung Members