Why do results differ for a User during consecutive FaceScan's?
Two factors could influence differing results between scans. The first is that the human body is constantly changing. The second involves environmental factors including sitting vs standing, posture, lighting and the light direction, the distance of a face from the camera, face angle, Internet connection, and beverage and/or food intake.
In general measurements of any form (digital or physical) will not be consistent between captures. All measurements suffer from a natural deviation because of the nature of measuring the human body, for example, if a person repeatably measures themself with a tape measure they don’t get the same measurement every time due to breathing.