I am in the middle of switching from SmartThings over to Hubitat. I am experiencing the same issue with geofence in the mobile app (iOS 15.6.1 on iPhone 13 Pro). Hubitat seems to only update once and a while, but rarely for me or my Wife. It doesn’t seem to be updating in the background. My wife never opens the app and hers never updates and mine only if I have opened the app very recently or use the Send Geo Event.
I am actually running SmartThings geofence as well as Hubitat’s and SmartThings is working fine and consistently updating my presence when I come and go, Hubitat is rarely updating, if at all. I have confirmed that I have the iOS settings the same for both.
I really hope this issue can be resolved and will gladly offer some of my time to help troubleshoot/test, as i use this feature in a bunch of my automations.