Same, I just got the S21 Ultra this week and have Had nothing but issues with the face recognition and fingerprint recognition. I've even saved multiple facial recognition slots and fingerprint recognition slots. I really hope Samsung get this fixed soon. It is really annoying.
If you are having some difficulty, here are some facial recognition tips.
Glasses, hats, masks, makeup, bangs, and beards can affect the recognition process.
Make sure you are in a well-lit area and the camera lens is clean.
For best results, make sure your image is not blurry.
Face recognition is less secure than Pattern, PIN, Iris, or Fingerprint.
Your phone can be unlocked by someone that looks similar to you (such as a twin).
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