Facebook Inc said it had underreported the number of views on iPhone of content published by some publishers using its Instant Articles platform between September 20 and November 30.
Publishers make money through ads on their posts.
Facebook said on Friday that a recent update to one of its metrics had led to the issue and affected publishers using one of its legacy platforms. Traffic numbers for iPad and Android devices were not affected.
The company apologized in September for an error in the way it measured a key measure of video viewership that significantly amplified users' viewing times on its platform.
The latest issue has been fixed and updated estimates will be provided, Facebook said.
Facebook also said it was updating the way it calculates potential audience size for ads as a way to give advertisers a better view of the number of people they can expect to reach.
© Thomson Reuters 2016