Give this a shot; https://www.samsung.com/us/support/answer/ANS00077687/
I have seven locations set up for my 700 square foot apartment and it doesn't work. Nothing works, despite trying methods on this forum and all over the internet. Why doesn't Samsung actually fix the problem instead of letting it fester on forums?
I finally fixed this (for me anyway). In location settings my phone was set to "high accuracy" but there is an option just below that called "improve accuracy". In this section you can choose bluetooth, wifi or both to scan for nearby objects even when those features are off. I set up the wifi option and suddenly the Smart Lock started working.