Oh good, this wasn't just me. Android user here, when using the mobile site with Chrome I'd occasionally get these hijack ads as well. I couldn't even back out of them, the only way to clear them would be to close my browser and re-open. The strange thing is they would happen on specific pages, not just randomly. I don't know if ads are a problem on desktop because I always run ad blockers.
I've since switched browsers to Firefox Mobile with Ad-Block Plus and haven't had issues since. I find it ridiculous that whoever runs the site has the gall to ask us to whitelist them while they host incredibly intrusive, potentially harmful ads. For shame, GamePress.