Geofence Arming Reminder and Multiple Phones

We set up arming reminders based on geolocation. My wife and I both have the app. We enabled both phones in the rule, so my understanding was “If multiple devices are selected, the rule will be triggered when the last of these devices enters or exits the geofence.” This morning I left and my wife was at home but we got a reminder - did I do something wrong?

At any point, did your wife’s phone turn off between when you setup the Geofence and when you left this morning? If so, the app needs to be turned on again when the phone powers up. If The app and its Geofence service are not running when you leave the fence, her phone would not be found within the Geofence and the reminder is sent.