Google announced that app interstitial ads that cover a “significant amount of content” on your page will be considered NOT mobile-friendly and will not rank as well as mobile-friendly Web pages.
Google said this will kick in on November 1, 2015, but the mobile-friendlytesting tools will show them as not mobile-friendly today.
After November 1, SEO updates, mobile web pages that show an app install interstitial that hides a significant amount of content on the transition from the search result page will no longer be considered mobile-friendly. This does not affect other types of interstitials. As an alternative to app install interstitials, browsers [should] provide ways to promote an app that are more user-friendly.
So the native Apple-supported Smart Banners and Google Chrome-supported App Install Banners are all mobile-friendly with Google. It is just the big ones that cover a significant portion of your content that are not mobile-friendly.
Make sure to test your pages that have app interstitials to see if they pass the mobile-friendly test, or check out the mobile usability test. These two tools will show you immediately if you have problems with ranking and app interstitials.
Google also said that only app ads that block content like this can cause a mobile ranking decrease. Other ads not for apps are apparently fine. From its post: “This does not affect other types of interstitials.”
Go to our Google mobile-friendly page to learn more about the mobile-friendly algorithm.