Google’s John Mueller posted a PSA yesterday on Twitter saying that with the mobile first indexing rolling out, that if you have app interstitials and if those are taking up all your content, then that is what Google will see. He said you are are roboting them out or replacing your homepage with it, then that is what Google will see.

Here is the tweet:

In short, check what you see on mobile and even use the fetch and render tool in Google Search Console. That is what Google will see on mobile when they do mobile-first indexing. So make sure Google can see your primary content!

This is in addition to the app interstitials penalty from back in 2015. Those are more sneaky than just normal app interstitials.

Forum discussion at Twitter.