Here's the deal: Google isn't happy with you.
Google's goal is "to help users quickly find the best answers to their questions, regardless of the device they’re using." In a recent article, Google discussed how popups are intrusive to users -- basically, if a user goes to your site because they clicked on a link that hosts content they're interested in, and instead they're greeted with a popup that's hard to exit out of, that's not cool anymore.
According to Google, intrusive interstitials frustrate users, and provide a poorer experience than when content is readily available. The need for accessibility is especially important in relation to the mobile user experience.
"So Google's annoyed, how does this affect me?"
As of January 10, 2017, pages where content isn't easily accessible to a user on the transition from the mobile search results won't rank as highly. Translation: if a user goes to your mobile site and the first thing they see is a popup, your search rankings crash and burn.
Every site these days seems to utilize popups, so to stay ahead of your competition, and save your search rankings, you'll need to act fast. As of right now, no one has a great solution to Google's changes -- except us.