Not trying to toot my horn here, but did you see my post about testing to figure out what the cause of the issue is?
A great example - my wife works from home a lot. Sometimes she turns wifi off on her phone. The way the cell towers are in our area, Find My iPhone sometimes shows her at Philadelphia International Airport, which is about 4 miles away as the crow flies (as they say). Now, she could be meeting a secret boyfriend who is a pilot for some quick rendezvous, but I’ll give her the benefit of the doubt and blame it on bad triangulation.
The above error happens quite a bit when she has wifi off, but it only happens at home. When she is at work with wifi off, her location is accurate. So, I also think some of this may be problems with the data used for triangulation.
Again, the first step in troubleshooting this is process of elimination. Use something like location based reminders and see if they “fire” at the proper, or improper, times.
Personally, I have not had one issue with location on my iPhone and SmartThings since I got it…unless my internet is out or ST was down for some reason.