It happens to me some. The only thing I have found that works is letting the page completely download before trying to scroll down the page. The other thing you need to do is go into your settings and clear your history and cookies. Once that advertisement pops up it will follow you from site to site.
I asked Matt to have the forum software checked to make sure it is not coming from us. In any case don't click, or provide any information to the spammers. If you see this popup on different websites your phone probably got infected, or has a malicious app running in the background.
I tried on my PC, Android, and iOS, but can't reproduce the problem.
Still looking into this. Matt scanned all the website files, and it all came clean. Looking at the picture, when the popup shows up, I can see there is a URL at the top. Can't read it...something template.club.. can you please let me know what it is when you see it again. Thanks.