Fingerprint scanner GT-511C3: All fingers are removed suddenly

I am using Fingerprint scanner GT-511C3 with Adafruit feather for my project. Everything works perfectly but I found registered fingers are removed suddenly after giving some one. They have no access to code level but only a product I made. How could this happen? Any possible scenario and solution to prevent this issue later?

I never had this issue while developing for couple months. It happened with the person by using two different products and all of them lost finger data but another person had no issue.