Thats exactly what happened to me , (dec Os update) did a factory reset and brought the finger options in settings and managed to get it working for another 3 days and they it disappear again. I contacted LG and within a week i had my phone back with new fingerprint scanner and main board according to what they said ( proven by a new IMEI number )
I had a spare phone for that week, I did sent the phone on a thursday and came back the following wednesday, could well be 3/4 days if you plan it to be pick up on a monday.
Thats exactly what happened to me , (dec Os update) did a factory reset and brought the finger options in settings and managed to get it working for another 3 days and they it disappear again. I contacted LG and within a week i had my phone back with new fingerprint scanner and main board according to what they said ( proven by a new IMEI number )