Traffic lights not allowing enough vehicles through

The traffic lights controlling traffic heading south towards Didcot always used to stay on green long enough to clear all/most of the waiting traffic. Something has changed and now only about ten cars can go through, which meant today traffic was queuing back onto the A415 junction and in turn causing much longer queues in all directions approaching Clifton Hampden. Some green cycles on the A415 only two or three cars got through due to queuing traffic on.the junction.

This may be a faulty sensor as for many weeks when you approach the bridge traffic lights towards Didcot it takes 30 seconds to change even at 3am when there is noone coming from the other side.