Guys at Merj discovered a bug in the Google AdSense platform that affects how AdSense understands and targets ads on webpages.
When AdSense bot crawls a webpage to analyze its content for ad targeting, it uses the “Mediapartners-Google” user agent to fetch the initial HTML.
However, when requesting additional resources (like scripts, stylesheets, images) to render the page, it switches to the “Googlebot” user agent.
If the website’s robots.txt file blocks “Googlebot” from accessing certain resources that are allowed for “Mediapartners-Google”, it can lead to incomplete or blank page rendering for AdSense.
While the bug is specific to AdSense, it could indirectly impact SEO by skewing data in server access logs.
When “Googlebot” requests resources for AdSense rendering, it can appear in logs as organic crawling activity, even for pages blocked in robots.txt.
This can muddle log analysis and lead to incorrect conclusions about Googlebot’s crawling and rendering behavior.
However, the bug does not directly impact how Googlebot crawls, indexes or ranks webpages.
https://merj.com/blog/discovering-and-diagnosing-a-google-adsense-rendering-bug