This month, many publishers began the year with low coverage of ads on Adsense. An issue spotted by Barry Schwartz, on Search Engine Seroundtable. Publishers complain that AdSense ads aren’t always displaying.
Despite the high number of posts on the forum, Google did not reply to the messages. Users with access to the support got an answer that the “tech team is was still investigating the issue.” Adsense publishers also reported a decline in RPM.
The reason for the low coverage, between 50% and 70%, was reported by Ginny Marvin, on Marketing Land: Google made changes on GDN that are impacting publishers, and the main change is related with the crawler and classification. Seems that Google is not displaying ads on pages not crawled by the Adsense bot (User-agent: Mediapartners-Google).