Same issue for me. Sensor will be working fine, then suddenly will stop working when trying to wake screen. After unlocking phone with pin, sensor will still not work until rebooting device.
I'm on Verizon and have the gesture and Samsung pay features turned on. The issue happens about once every other day.
I have exactly the same problem. I hope Samsung solves it as soon as possible and this phone doesn't end like being a disaster like samsung note. I switched from Apple to Samsung and I get a non-working fingerprint sensor.
I have had the same issue. S8+ and sometimes even after restart (after putting in psw first time) This is ridiculous... Yes I am putting finger in right place... Pls fix ASAP.. Very annoying.. Don't want to use retina as it probably drains more battery..