Have it set to high accuracy, I know I basically have no cell tower near me, think the closest is about 5 miles, but the location and smart lock worked perfectly until an update a little while back, did a factory reset last night so crossing my fingers
It also seems that the Google Maps light blue circle or the dotted line which is shown when one defines the trusted location has nothing to do with the actual "what is considered as a trusted area" concept. This morning my phone refused to understand that it was home again and I did test adding 10 close by spots (moving the found pin and picking points outside around the house) around my house an suddenly phone started understand that it, indeed is in a trusted environment. ; )
I have now investigated this issue further. In my phone I must sometimes restart the phone in order get trusted locations work again. In another newer edition of same phone model this is not needed. I did check which position Google Maps most often finds when I am at home and defined that as a safe location (that is in the yard outside of the house). There might still be some operating system bugs that may require occasional phone restarting.
I did post earlier that clearing Google Maps - Storage Cache solves this problem.
Sometimes phone may still require a restart after the smart lock has been operating flawlessly for days.
After this restart you may have to clear that Google Maps - Storage Cache again.
Here is a handy way to do this:
1) Open Google Maps and let it locate your position you have marked as a Trusted location
2) Open Multitasking Menu (usually the left side of the Home button)
3) Hold your finger on little Google Maps Icon on left side of the Maps window until it opens Google Maps app Information icon on the right and, when you touch that it opens panel where you can Open Storage and clear its cache. In older Androids it opens this panel directly when holding finger on Maps icon, in newer via little info ( i ) icon.
Cleared the cache before, probably when you posted before but going to give it a shot again, got the update last week so maybe the combination will fix it plus did a factory reset the other day, so cleared cache, restarted, cleared cache. I know doing the multiple spots seemed to help but it would be nice to not have a list of coords for one place.
Well, I did test adding multiple trusted locations around my house using the placed using the Placed Pin option.
When I walked away from my home Trusted Locations System went bananas and ended up thinking that I'm home all the time even half a kilometer from my home.
I had to remove all those extra places and use the one and only location which Maps always finds first when I'm at home. In your case I would use only a couple of most commonly found places where the system locates you at home. Otherwise the system may end up practically disabling the pin code protection.