On iPhone 5 (wife’s) and 6, mobile presence has been pretty stable for me.
One issue that I face here in NJ is the 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 would crash at times or will still be updating the status while I am already in my geofence and reach my house. Didn’t happen everyday (may be depending on the load) but this was one of the reason for me when it did not work for me.
On my way back home from office, I disable Optimum wifi on my phone to get around and the it triggers at the exact spot every day near my home.
But when leaving for work in the mornings, it triggers at a different spot. The reason may be I am still connected to my home wifi when I leave and as I go further away from house, the signal obviously drops and as soon as my wifi drops me and LTE takes over, I get the left home notification I have set.
Exact same behavior on my wife’s iPhone. So, basically in my case it was the slow transistion from wifi to LTE and vice versa causing the issue.
Note: And of course I am sure you have ruled out the usual suspects. Ignore the setting up part of the second account in the linked thread…