I have the same problem. It seems like if the sensor gets wet/dirty/sweaty it stops working (even after cleaning it) and rebooting the phone. very frustarting. I was just getting used to it being on the back of the phone.
I'm having the exact same issue. Only had my phone for three days and it started unrecognizable. Seems as though this is a software problem because the S8 and the S8+ are having the same issue. This sucks! Samsung, please fix this issue! We love the Galaxy line of phones, don't force us away from them with these petty issues!
Has anyone else tried the dialer fix. i am trying to find root causes//better fixes but you guys arent trying my methods! I would test by myself but fortunatley i dont experience the problem as often *Knock on wood*