At some point during early September 2017, the Google Plus button has been updated and they have also removed their API endpoint, which used to display the current number of +1’s/shares on the buttons and third party social signals counters. Prior to the update, Google made these changes public on their official developers plugin page: https://developers.google.com/+/web/+1button/
Furthermore, a Google employee (John Nack) also made a post on his Google+ account, explaining why they are making these changes:
Will this effect orders?
This update is similar to the one Twitter made back in November 2015. Fortunately, our system allows us to track the number of Google+ shares we deliver during each promotion and we compile them in the reports.
However, once we complete the campaign, we are no longer able to view the websites current Google+ stats, as they are no longer available (post API update). This is why we will refer to the Google+ as: “0” on our initial reports, since we can only count the amount delivered during each separate promotion.