Google is cleaning up the mobile experience...
"To improve the mobile search experience, after January 10, 2017, pages where content is not easily accessible to a user on the transition from the mobile search results may not rank as highly.
- Showing a popup that covers the main content, either immediately after the user navigates to a page from the search results, or while they are looking through the page.
- Displaying a standalone interstitial that the user has to dismiss before accessing the main content.
- Using a layout where the above-the-fold portion of the page appears similar to a standalone interstitial, but the original content has been inlined underneath the fold."