Google has officially confirmed they have begun rolling out the intrusive mobile interstitial penalty yesterday. Google warned us that this was coming almost a six months ago, and it did start rolling out on January 10, 2017, as Google promised.
Google’s John Mueller and Gary Illyes confirmed the penalty began rolling out yesterday.
This penalty only impacts intrusive interstitials that happen directly after going from a Google mobile search result to a specific page. It does not impact or penalize pages after that, so if you have a intrusive interstitial that comes up later in the click path on your website, this won’t impact it: it only looks for the intrusive interstitial after the click from the Google search results page.