I had the same fading issue with my iPhone 5S after 7.1. I brought it into the Apple store, the Genius ran his diagnostics and within a couple of minute replaced my iPhone. Seems to work better but I still have problems with my right thumb fading in a day or two, while my left index is always consistent. Must be a problem with my thumb, although I don't understand why it would work great for a few days and then not work at all.What people's experience on getting their 5S replaced with a fingerprint sensor that is losing it's consistency even on 7.1. Do they replace the phone and have you pay the fee or do they just fix the part?