Also, I am sure you have already checked:
Enable Location Services and Background Refresh for SmartThings app.
(Settings -> Privacy -> Location Services -> SmartThings -> Always)
General -> Background App Refresh (On) -> SmartThings(On)
Some others have reported too if the phone is locked, it somehow acts erratic. Cannot confirm it. My wife has the app running always on a 5 but the phone is definitely always locked when she is arriving/departing. Will check on my iPhone 6 today.
One issue that I face here in NJ is the stupid Optimum auto hotspots all over the state (even though saves me a lot on data plan). I have my phone registered to auto sign in to Optimum hotspots being an Optimum customer. These hotspots have very weak signal near my home. As a result the ST app will crash at times or will still be updating the status while I am already in my geofence and reach my house. Doesn’t happen everyday (may be depending on the load) but this is one of the reason for me when it does not work for me. On my way back home, I disable Optimum wifi on my phone to get around.