Since the original post I’ve reboot the Iro and changed the start time to 12:30am. I’ve done no manual watering for weeks nor made any other changes. The zone in question is not in any other currently active schedules. The good news is that it has not watered since and the graph is back to what I’d expect so I suspect the reboot resolved it. Though it could have been a quirk with the scheduling time as I had only switched to using 4am instead of sunrise a few months ago.
I have the zone set to slight slope, it didn’t do a cycle/soak but I don’t see that as a problem. The water only drains to the street an hour or more after watering, so it’s not direct/surface leakage. The water instead soaks through the lawn, hits the clay soil before soaking into the drainage system which carries it out to the street. It’s a pretty fine line between adequate watering w/o leakage. Generally if Iro thinks the zone moisture balance is greater than 100% then it’s likely leaking water that day.