There has been an update on March, April, and May, and the may update was perhaps a smaller scale one, which they were trying to change the dynamic meta description from 300 to 140-160.
I think the change has surely affected the sites - pages that have auto-generated meta descriptions were mostly affected, as these auto-gen metas + shortening of the dynamic meta by G, has reduced the amount of displayed data in the meta description, and hence making the site less visible due to lesser keywords being displayed.