The smart lock on my S9+ was not workng correctly either. I entered the actual address and the circle around it on the map was correct, but the feature would not work. I edited the address using latitiude/longitude coordinates and had the same problem. Finally, I eliminated both addresses shown and used only a GPS signal (by tapping on the map shown for my current location). Once entered, i restarted the phone and the smart lock finally worked.
I just almost lost it trying to fix this.
Finally I deleted the GPS. I couldn't remove the Google Home address But I turned that off too restarted Turned the Google Home address (should work with GPS location too) then I powered off.. Don't just restart because that does nothing.
I rarely power off my phone but I guess I should start.