Facebook Inc. said it is working with comScore Inc. to update its metrics after the measurement company pointed out a mistake in reporting of mobile traffic from Apple Inc.'s iPhone users.

The social networking giant said that due to a recent software update, it had undercounted traffic from some Instant Articles publishers from Sept. 20 to Nov. 30. The error affected Instant Articles publishers including the Washington Post, BuzzFeed, Mic, Entrepreneur, Foreign Policy and Variety, The Wall Street Journal reported Dec. 16, citing a person familiar with the matter.

The social networking giant recently announced details of four additional user-engagement metrics that it had been misreporting to marketing clients, following its admission in September that it had overstated the average viewing time for video ads by as much as 60% to 80% for two years.