The top cap of that sensor will come off with a slight twist and pull upward. Something (bugs, debris) may be under the cap pushing the micro switch. Take the cap off and see if that message stops. If it does, clean the cap and sensor area inside where the cap came off and put it back on.
If you see the message again, check the wiring.
There may be a wire broke or loose splice between the sensor and the controller. That doesn't look like the original sensor wire that is connected to your Rachio controller, look for a splice on that wire between the controller and sensor. That may have been why it was disabled on your old controller.