Many Facebook advertisers woke up to a shock on Sunday morning, with a bug in Meta’s ad delivery system causing significant overspend on a range of accounts.

Some ad buyers reported CPMs up 200%-500% versus the previous day, while all ad performance metrics were seemingly affected. Other advertisers also reported their ad sets well exceeding their daily set budgets, with no way to limit the damage.

Meta acknowledged the issue within hours of reports coming in, and quickly worked to implement a fix, while also assuring ad partners that credits will be issued to rectify the situation.

As of 9:45pm ET, Meta had reportedly fixed the problem, and all ad systems were functioning as normal once again. Meta says that it will communicate with impacted ad account managers directly in the coming days.

It’s a significant error for the platform, which has been working to improve trust in, and reliance on its ad products in the wake of Apple’s iOS14 update. With many users opting out of data tracking, Meta has had to re-align its ad delivery process around machine learning, and improved detection of the best audience for each campaign.

Those efforts have been delivering results, but issues like this will make ad buyers more wary of Meta’s systems, and could prompt a scaling back of ad spend.

In all likelihood, those impacts won’t be long-lasting. But essentially, it’s another headache that Meta doesn’t need as it works to reform its ad systems in line with new requirements.

It’s worth checking your Facebook ad sets, and ensuring you haven’t ended up overspending across the weekend.

We’ll update this post if/when we hear back from Meta on potential rectification steps.