Facebook told some of its advertiser clients Monday that a "bug" in its measurement system caused it to undercount the performance of ads it served served to certain iPhone users since February.
As earlier noted by mobile ad consultant Eric Seufert on Twitter and confirmed by Insider, Facebook told advertisers that the measurement bug was spotted and fixed on August 20.
In communications with advertisers, Facebook also said it was still investigating the matter, which concerned the way Facebook interacts with Apple's privacy-focused measurement solution, SKAdNetwork. It's a platform more mobile advertisers have come to rely on of late following Apple's new AppTrackingTransparency privacy update that rolled out in April.
The bug caused Facebook to undercount whether ads served to iPhone 12 users on the Facebook app led to users downloading advertisers' apps. It didn't affect Instagram or Facebook's Audience Network of third-party apps.
In a statement, a Facebook spokesperson confirmed the company fixed a bug "that led to under reporting of some advertisers' conversion metrics."
"Based on our iOS user base, we believe around 10% of total SKAdNetwork conversions were not counted or reported," the statement continued. "The impact on specific campaign metrics will vary. We are communicating with advertisers whose metrics may have been impacted to make sure they are aware"
Mobile ad experts told Insider that while many marketers tend to prefer Facebook's Audience Network to drive app-installs versus Facebook itself, the error — and that it went undetected for so long — could have caused advertisers to miscalculate where they should have been spending their ad budgets. An undercount also could have hurt Facebook; advertisers may have shifted their dollars to rival platforms if they thought their campaigns were underperforming on its app.
Analysts from Counterpoint Research said in June that Apple had sold more than 100 million iPhone 12 handsets by April this year, seven months after the launch of the series.
If Facebook wasn't receiving full information about app-installs from owners of Apple's latest iPhone model, "then the highest value group of users wasn't being accounted for in campaign performance," Seufert told Insider.
Seufert estimated that somewhere between 20-30% of US iPhone traffic comes from iPhone 12 devices and that he expects ad performance to significantly improve for Facebook iOS app-install campaigns now the error has been fixed.
Aaron McKee, chief technology officer at location data technology company Blis, described Facebook's app-measurement miscue as "a big deal, but perhaps not apocalyptic" for mobile-app advertisers.
"Every company occasionally makes mistakes, but situations like this highlight that marketers may be overexposed to the fallout if they are only relying upon a single large advertising partner," McKee said.
This isn't Facebook's first measurement snafu. The company has on several occasions in recent years been forced to apologize for overcounting or undercounting the metrics it provides to advertisers and publishers. In some of those instances, Facebook has issued refunds or credits to affected partners. Refunds will not be issued this time, according to a person with direct knowledge of the matter.
The company is also currently facing a class-action lawsuit, originally filed against Facebook in federal court in San Francisco 2018, that claims the social-media giant inflated its "potential reach" advertising metric to dupe advertisers.
