Wait button cuts out and reverts to car traffic

Today I experienced a problem on both sets of the pedestrian lights crossing Pentonville Road. Your press the pedestrian wait button and it lights up but this sometimes cuts out within 30seconds and the green light of course does not change. It seems to give priority to car traffic over pedestrians crossing as I experience this problem at the lights only during the car rush times. I waited 10mins at around 3.15pm today to cross the east direction traffic as it took 5 mins for a the light to finally change (after constantly repressing the button each time the light went out) and wasn’t able to cross as traffic blocked the crossing so I couldn’t get my baby across in the road in the pram. Finally after another 5 mins I managed to cross. This crossing has had this problem for a while but it isn’t safe. The whole crossing should be reviewed as it makes it near impossible for pedestrians to get across sometimes (yellow boxes would be helpful to stop cars blocking the crossing).