OvertureRep has confirmed the recently reported bug in the Yahoo! Publisher Network reporting engine. WebmasterWorld has several posts stating that publishers are noting very low impressions as compared to other days.
Overture Rep (YahooSarah) said- "Thanks for reporting your findings here. Today, we found an error in our YPN portal that caused inaccurate reporting of Ad Unit Impressions, CTR, CPM and Average RPC data for some of our publishers.
Number of clicks and Revenue reporting for all publishers is accurate and was not impacted by this error. We have issued a fix for this error and you will see accurate data going forward within the next 24 hrs.
Sorry for the inconvenience and we appreciate your patience.