There are some Google AdSense publishers that have been noticing changes in ad delivery on their sites over the past month or so.  Publishers say ads aren’t being served and the ad slots on their pages are appearing as blank spaces, which in turn, is causing drops in revenue.

There has been some speculation on the AdSense forum that the issue could be caused by policy changes, or by dynamic pages or URL parameters, or when a new page has not yet been crawled by the AdSense bot. It turns out that last guess is closest to being correct.

Google has been tinkering around, making changes to buying processes on the Google Display Network.  Because of this, Google won’t automatically monetize sites or pages that the AdSense bot can’t crawl.  The AdSense crawlers categorize, classify and label content for monetization.

Consequently, the issues some publishers are experiencing may be the result of not properly granting AdSense crawler access to their sites.  According to Google, the problems aren’t widespread, but the changes, which are still in the early stages, are affecting some publishers more than others.

If you’re one of the people who is experiencing with this, and there isn’t a policy violation notice in your AdSense account, check the crawler access error tab located under “Status” in AdSense for notice of crawler implementation errors.  A possibility that the crawler is being blocked in the site’s robots.txt file (see details in this Help Center article) or getting tripped up by when content is served behind a login (see how to give access to login-protected pages here) or even getting tripped up by when content is served behind a login (check here to see how to give access to login-protected pages).

Google is working on identifying publishers that are impacted in order to help them resolve issues and will be issuing further guidance in the short term.  The team will evaluate results of the early-stage changes over the coming weeks.

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