We've changed how quiz data is stored - timeline-based analytics are now available starting April 4th, 2018.
If you have quiz analytics data before April 4th, 2018, you can still access all the statistics and downloadable lead data in the Legacy tab. Watch the video below to see how:
Prior to the April 2018 analytics update, a new version of analytics was created every time you published your quiz. Some of those analytics time periods spanned several days and couldn't be translated correctly into a timeline format.