Twitter's ad revenue growth dropped to single digits over the summer and estimated that recent bugs have cost the company at least $24m in lost income.
The microblogging platform posted third-quarter overall revenue of $824m (£639m), up 9% year on year – lower than the 21% growth posted in the previous quarter.
Twitter said its performance between July and September was negatively impacted by steps it took to fix "bugs that primarily affected our legacy mobile application product". This affected the platform's ability to target ads and share data with advertisers and audience measurement companies.
In August, Twitter apologised after revealing user data was shared to advertisers without permission and, earlier this month, expressed regret again for a similar mistake. This followed an admission in May that some user accounts’ location data was being shared with an advertiser partner during real-time bidding auctions.
"We believe that, in aggregate, these issues reduced year-over-year revenue growth by three or more points in Q3," Twitter wrote in a letter to investors today. With Twitter's revenue totaling $789m in the third quarter of 2018, 3% represents $23.7m.
The company warned that these issues are likely to affect its ad sales performance in the fourth quarter, which comprises the busy holiday period.
Twitter also blamed "greater-than-expected seasonality" in July and August, the summer holiday months that usually mean a slower period.
Ad revenue, the vast majority of Twitter's total revenue, grew by 8% year on year to $702m – considerably weaker than the 29% growth recorded in the same period last year. The smaller "data licensing and other revenue" income stream grew 12% to $121m.
The company is continuing to perform more strongly in the US, for which revenue was up 10% year on year to $465m, while revenue from the rest of the world was up 7% to $358m. More than a third of Twitter's non-US income comes from Japan ($129m).
Twitter said its video ad formats "continued to show strength", particularly in-stream ads and its Video Website Card that allows users to click through to discover more about a product after watching a video.
However, the company is still reliant on large- to mid-tier customers representing a "sizeable majority" of its ad revenue.
User growth, which Twitter defines as "monetisable daily active users", was 145 million, compared with 139 million in the previous quarter and 124 million in the third quarter of last year.
Twitter said its key priorities for improving the platform remain the same: health (help people find "credible" information while feeling safe); conversation (making it easier to discover content and chat with other users); sales (improve the ads platform); and platform (data security and user experience).
Jack Dorsey, Twitter's co-founder and chief executive, said: "We’re continuing to improve relevance while testing ways to make it easier for people to find what they are looking for on Twitter. We also continue to make progress on health, improving our ability to proactively identify and remove abusive content, with more than 50% of the tweets removed for abusive content in Q3 taken down without a bystander or first-person report."