If you are using a vivo phone, facial recognition uses the front camera to take a photo of the face, and compares it with the facial data that has been recorded in the phone. When multiple facial feature points match, the unlock can be successful. When you close your eyes or wear a mask, some facial feature points can still be successfully matched, so the phone can be unlocked. This does not mean that the phone is malfunctioning and can be used with confidence.