This sounds almost too mysterious to me: on the microcontroller, the pins for sensor inputs have internal pullup resistor turned on in the firmware, if this was caused by interference, it’s gotta be really strong interference that can overpower the pullup resistor. I can’t imagine how this could happen.
What if you change the sensor type to ‘Rain Sensor’ — do you just get randomly flipped rain sensor status? If os, I suggest that you send a support ticket and arrange for it to be sent back to us so we can check what’s going on.