About two weeks ago, Google stopped showing the Things To Know box in the desktop search results but don't fret, it seems to be back now. RankRanger's tracker tool spotted that the Things To Know box has returned to normal levels within Google Search.
Here is the chart from RankRanger showing it is now back to normal levels:
Shay Harel from RankRanger notified me of this on Twitter saying "Although the Things to Know SERP feature disappeared on desktop on July 19th... It's back!"
Forum discussion at Twitter.