I have had this kind of problem, but much more random times between switching. I disconnected and reconnected all the wires allowing the wires from the signal to hang as freely as possible without being tangled. . There was some strain on them before. This appeared to cure the problem and it has not happened for a long time. I have no idea why. This signal also had the problem of the arm not moving when the motor acts ,which was cured by flicking the arm as recommended by Dapol Dave. I have bought 3 signals since, which are much smoother and quieter than the problem one and have worked without trouble. Maybe it was a rogue example or later batches are a better build. They are all 00 GW type. .