A followup, in which I hang my head in shame.
One of our front yard sprinklers had it's head cut off by an inattentive lawn guy. Major geyser.
When we had the sprinkler repair company come out, they found two breaks in the underground pipes and fixed both.
It's an old computer nerd mantra, "whoever touched it last broke it", but that's not always true.
It will be interesting to see what happens the next time the Rachio decides to water.