For what it's worth, I was able to eventually get to the bottom of my problem. Basically it came down to the GPS coordinates for my phone location not reflecting my actual location, particularly when it is first turned on in the morning, so that the Smart Lock pins weren't in my GPS circle, even when I was in my house. I observed this by opening Maps and waiting for it to find my phone (the grey dot becomes blue and starts roaming around). Even once it got a lock, it took 15 minutes for it to come close to where I was actually located in my house (it would be down the street, then hover to my front yard, then to the back yard, etc, all while I was sitting still in my living room). For some reason, after traveling somewhere (e.g. to work) the accuracy of the GPS improved, so that when I came back home in the evening it had a better sense of my location, so the Smart Lock pins I had stuck around my actual house were in my GPS circle when I was physically in my house. If you really want the Smart Lock to work, you have to put down like, 50 pins (I did mine in a grid from the street all the way to the back yard); that way the odds are high that at any given time, one of them is in your GPS circle. I did this and it solved the problem (annoying though).
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I have this exact same issue. In order to get it working again first thing in the morning, I have to repeat the step of dragging the pins around. So incredibly stupid. I don't understand this "four hours of inactivity" thing. Why is that even a feature? It seems to be causing the entire problem.
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