A recently installed bHyve timer has shown the same issue with the external sensor that has been reported in many posts. I have a wireless rain sensor that has a relay switch, so it is a true open/close output. Noticed that when the sensor is on (open circuit) the timer reports that watering is suspended due to a sensor, but then the water zone oscillates on and off at about a 30 second interval. When I remove the 18″ wire the connects the rain gauge to the sensor terminal, the timer operates correctly and halts watering. A classic issue of an overlooked hardware design and a bias issue. There is about a 1 volt DC bias on the sensor terminals, indicating that this is connected to an input logic devise such as a transistor or IC.
The problem seems to be that connecting a length of open wire to the sensor terminals is sufficient to create a feedback loop and cause the timer to pulsate the watering. Without knowing the circuitry behind the sensor terminals it is difficult to propose the best solution. Using a wireless sensor, as I am, the work around is to add a 0.1 uf cap across the timer sensor terminals. This seems to isolate the 18″ of wires to the rain sensor base. If someone is using a wired sensor with many feet of wire between the timer and the rain gauge, a capacitor may not work. As mentioned, this s a hardware issue and may not be able to be solved with firmware update.
Hope this helps those with this issue and the Orbit engineers to add proper decoupling on the sensor terminals.