Sadly, last night after a couple days of working perfectly, everything failed. The zigbee presence sensor first failed to find me arriving home, and then, based on activity logs, did show as arriving, but the event did not fire.
I went to plan B, which involved doing something directly through the mobile app, but the dashboard would not load so nothing was available to me.
That left me outside, in my wheelchair, at 10:30 at night, in the rain, unable to get in my house.
Fortunately, my housemate was home, and I was able to get him to come let me in.
After this experience, I do not feel I can trust smartthings at the present time for anything except pure convenience use cases.
It’s just a safety issue. 
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So I am not going to do any more work with the occupancy concept at the present time, and I am removing everything from my installation that depends on ST geolocation, Although I am still using some geolocation from other apps. Just not with smartthings.