here are my observations.
a geotagged reminder failed to work so I have been reading the thread.
To attempt to fix the issue I turned off reminders in iCloud, reset location and privacy settings, turned on reminders in iCloud. i was asked (after a pause) if reminders could use location info. In Location Services a hollow purple location arrow appeared. it should have been solid as a location reminder was set up. I adjusted the geofence and the arrow went sold purple so i assume that the system was functioning correctly. I quit the app. arrow went grey. i restarted the app, arrow went hollow purple. i assume it was failing to recognise that there location aware reminder was in force. if i, once again, adjust the fence, the arrow in location services goes solid purple.
if you enable another location aware service (eg Siri) the reminders arrow loses its solid purple status.
With further testing, you do not need to actually adjust the geofence, merely get to the screen where you can see the geofence map.