This has recently been happening to me. I use Firefox and have NU as a pinned tab that it open 24/7. Every once in a while when I go to the tab what appears isn't the NU homepage but a white screen with a strange URL in the address bar that contains "advertisingenergy.com" in it. The reason for the white screen is because Firefox identifies it as a pop-up or something similar and doesn't allow it to load without the users permission. I'm assuming this caused by one of the ads on the site based on the appearing URL. This has happened about 5-6 times in the past 2 months, but I have never actually watched it occur. I have only seen the aftermath when I switch to the tab. FYI NU is whitelisted from the ad-block on my browser.
Here I's the place to report bad adds: https://forum.novelupdates.com/threads/reporting-advertisements.32118/ I'd try clearing your cashe first to make sure the problem is with NU, if you haven't already.
Those are called Redirect ads and they plague pretty much every ad network. The way ad networks are set up makes it hard to track down who makes the ads so site managers can only manually ban certain ads if they've got the redirect URL, which is different from the URL you're taken to after it's done loading or by trying to report it to the network. Since there's no way of tracking down who submits the malicious ads, you can't blanket ban ads from them and it becomes a war of attrition to get rid of them. Sometimes switching ad networks helps or hiring a dedicated team of people to whitelist/blacklist ads. There's also the issue of malware which can replace ads on sites with their own ads and ad networks that actively buy these kinds of ads because they pay well. So in some cases a site will have a ton of these kind of ads because they're using a bad ad network or your computer has been compromised by a virus or bad program. Worst time of the year is around holidays when ads sell for a premium so networks try to get as many ads as possible to maximize profit, normal ad or malicious. So around holidays even good ad networks might flood the sites using them with bad ads.