I've had this problem with increasing frequency lately, too (usually redirects to a page claiming I've won something from Google). Last time this happened I could avoid it using Firefox incognito. Always when I'm on 4G.
If you get an intrusive ad like this - it may still be possible to scroll to the bottom and use the "Report Ad" button to report it - I believe that captures the details about the ad and your settings and sends them to proboards to correct. I can't report myself without replicating it, but at least that link doesn't require you to set up a second account on the proboards support board.