It is quite possible that an electronic fault exists on the system and will probably be repaired as soon as the traffic department is notified of the problem.....
but there is also the possibility that the loop detector is not getting triggered because the vehicle in the front of the line is not positioned over the loop. Many drivers are careful not to trigger the red light fine camera and stop too far away from the front and in the process also miss the first loop that tells the system that there is somebody waiting on that side of the signal.