Broad beans plants but few pods

I sowed the broad beans at end of Feb. and planted out early April. They have grown well and I nipped the tops off when some blackfly arrived. Then I left them to it. I had a look at them Yesterday and there are very few pods at all.

Has anyone else had this. The only thing I can think of is the late frost in May. Is there any other possible cause?

I usually leave the beans to dry on the plant and use them in making humous. Still got plenty from last year so not a disaster but worrying - it reduces my safety stocks.