Google has made a change to its snippet algorithm. You can read about it here in an article from searchenginejournal.com.
In short, Google wants to ensure that snippets are current. It’s updated it’s algorithm to better understand which types of content could become stale and which may not. The takeaway from this is that Google, as always, wants the most relevant results first time, every time. As a result optimising your content accordingly can make a big difference to whether or not your content gets featured, and if it is being used, whether it continues to appear.