I'm beginning to think that the problem with the type of scanner that Google (or HTC and LG) uses is more humidity-sensitive than anything else. My 2 had problems for months when it started getting cold last year. 4 replacements (all sen back) had the same problem. Then, all of a sudden, the original one started working again, and I was able to add a fingerprint. Now it unlocks almost before I touch it. We'll see in November if it starts acting up again - then the "lick and wipe" starts again, until the humidity goes back up. (And it affects fingers more when they're older. 76 year old fingers make you think you have defective fingers.)