The rain sensor state can sometimes be a little confusing.
From what I see there I bet that on the 20th it was activated until 12:38pm, and then if get we too many requests in the same minute for the rain sensor, we don't allow some of those messages to come through since they can flood the server. The Iro will still behave correctly (not watering when the sensor is activated). We have also seen some bad wiring where the rain sensor is triggering every second. That massive number of events would really be a bad experience in the event history
So, there was probably another deactivate in that same minute. Sometimes if the rain sensor is dirty or drying out there can be a bit of noise.
Hope that helps.