So I was playing around with my security settings and have read that Smart Lock could be a neat feature. Problem on my cell is that I have enabled all the four settings in Smart Lock (On body, Trusted places/devices/voices) but outside of maybe once or twice, this feature works rarely or inconsistently. I can place my cell down on the couch and hit the power button and not have to swipe/finger print to unlock the screen.. a few minutes later I do the same thing and again get asked to swipe to unlock...I have to do this or use my thumb print.
I had the same issue and it's a known issue online as well. Samsung has noticed this with the S8 devices too. I would suggest redoing the settings again and if that does not work, contact Samsung and open a ticket with them.
Thanks Bud...did some extra searching and I have changed Battery Saver to Medium, and will see if this works..the revised battery seems to work as long as the unit is in my hands. The minute I put it down though I have to pin/swipe to unlock again.