I've noticed a number of alerts are missed, mostly speed alerts. For instance, I have an alert threshold set to trip at 75mph. I might receive 2-3 speed alerts for the day, but examining the logs I might find a significant number of excess speeds hits for which I never received an alert.
I've experienced several occassions where geofence alerts were missed as well. The track vehicle either entered or departed the fence and no alert was sent.