Google ads, Adwords and Double Click, will block flash ads from being uploaded by their advertisers starting June 30th, 2016. They have long encouraged advertisers to start using HTML5. It is because Google wants the ads to have better market penetration since Flash ads require Flash Player Plugin to be install on users computers. Starting January 2nd, 2017, any ads made on Flash will no longer run on Google Ads Network (Adsense, AdChoice) and Double Click.
Over the last few years, we’ve rolled out tools to encourage advertisers to use HTML5, so you can reach the widest possible audience across screens (http://goo.gl/nWHctK). To enhance the browsing experience for more people on more devices, the Google Display Network and DoubleClick Digital Marketing are now going 100% HTML5