(Bloomberg)—Twitter Inc. discovered a software bug that overstated how often video ads were viewed on Android phones, the latest snafu to shake faith in the measurement of digital advertising.

The company issued refunds to some clients who ran video ads on the Twitter Android app from Nov. 7 to Dec. 12. The bug caused views to be overstated by as much as 35%, according to a person familiar with the matter.

Twitter’s mishap comes after Facebook Inc. has struggled with several measurements problems that raised questions about the efficacy of online ads. Facebook so far hasn’t refunded clients. Twitter’s refunds were small, in many cases less than a dollar, said the person, who asked to remain anonymous because the information isn’t public. Business Insider earlier reported the news.

“Once we discovered the issue, we resolved it and communicated the impact to affected partners,” Twitter said in a statement, declining to say the value of its refunds. “Given this was a technical error, not a policy or definition issue, we are confident it has been resolved.”

Twitter has bet on video advertising to reverse a slowdown in sales growth. The company has struggled this year to get advertisers to raise budgets as the size of its audience stagnates. Twitter recently lost chief operating officer Adam Bain, who built its ads business.