My wife had similar issues a few years ago when words with friends became popular..... Constant pop up ads that her phone was infected with one thing or another. I almost did a FDR....but uninstalled every app that was ever downloaded from the Play Store and rebooted the phone. Then we installed only the apps that were necessary and never reinstalled words with friends and the problem never came back. I posted about it somewhere a few years ago, but might have been a different forum.