It's quite common that hosting providers have templates set for pages like 40x and 50x error pages but it's uncommon for those templates to have ads in them, or even worse, having malvertising that will blacklist your site.
On a recent case, we came across a scenario where Google AdWords was blocking a campaign of a website due to URLs from www[.]iyfipgun[.]com.
Upon closer inspection the URLs were coming from the template that the hosting provider had set for the 404 Not Found pages.This was the code:
If you are experiencing a similar report from any external providers such as AdWords, the template pages are the best place to start your investigation.
If this is indeed proven the culprit, a quick fix is to just force your own handle for certain pages on the .htaccess file such as:
ErrorDocument 404 "not found"
This means that it will simply display “not found” instead of showing the template page.