How does hazard reporting / warning work?

As an experiment, I stopped at a place in my neighborhood where the city dug up the street to fix a water leak, and left an unpaved area.  I called it a pothole, and "reported" it.  But when I rode by it again on the same ride, I didn't get a warning in either direction.  However, at the end of my ride, I was asked if the hazard was still there, or had been fixed.

What do I have to do to get a warning?  (I have seen warnings a couple of times for hazards reported by other riders, although I couldn't identify either of those hazards.  In one case, I was seeing a distance countdown until I was about 300 - 400 meters away, then it distance started going up!  I guessed that the hazard must have been after a turn that I didn't take.