If you track your site in the Google Search Console (and you should be) they have added a checkbox to see the number of impressions your jobs are getting. Just click the Job Postings link on the left nav to access, then check off the impressions box to see the data.
I was speaking to a client the other day who tipped me off to the new filter. Whats interesting though is that around the end of April, my sites took a big hit in impressions. I confirmed with a few other job boards that they experienced this dip as well.
So it seems the Google Jobs index had an update which knocked down total impressions. I can only guess why. Perhaps they are getting better at de-duplicating or some other factors are now involved. I have seen a small uptick in the past few weeks so my impressions seem to be trending back up but they are still down over 60% from April levels.
Check your stats and let me know if you have experienced the same by leaving a comment.