While trying to speed up its iOS and Android apps, Facebook accidentally stripped out too much data about news feed posts by Pages. This caused Page Insights to be misreported, leading admins to believe their posts reached fewer people than they actually did, in most cases. Bug fixes are now rolling out and accurate data will flow into Page Insights starting Monday.
WOW! We run a lot of facebook sharing campaigns and the change is huge! To bad it wasn't just a reporting error instead of a serving error. Our posts went from about 5% viral to about 150% viral. Again, too bad it means nothing as far as actual reach goes.