Fable, a popular app for talking about and tracking books, is changing the way it creates personalized summaries for its users after complaints that an artificial intelligence model used offensive language.

On Friday, trouble came for the commissioner himself: Federal agents arrived at the residences of Mr. Donlon, 71, a former F.B.I. counterterrorism official hired after his predecessor departed amid an investigation. They seized documents that he said had come into his possession about 20 years ago.

One summary suggested that a reader of Black narratives should also read white authors.

In an Instagram post this week, Chris Gallello, the head of product at Fable, addressed the problem of A.I.-generated summaries on the app, saying that Fable began receiving complaints about “very bigoted racist language, and that was shocking to us.”

He gave no examples, but he was apparently referring to at least one Fable reader’s summary posted as a screenshot on Threads, which rounded up the book choices the reader, Tiana Trammell, had made, saying: “Your journey dives deep into the heart of Black narratives and transformative tales, leaving mainstream stories gasping for air. Don’t forget to surface for the occasional white author, okay?”

Fable replied in a comment under the post, saying that a team would work to resolve the problem. In his longer statement on Instagram, Mr. Gallello said that the company would introduce safeguards. These included disclosures that summaries were generated by artificial intelligence, the ability to opt out of them and a thumbs-down button that would alert the app to a potential problem.

Ms. Trammell, who lives in Detroit, downloaded Fable in October to track her reading. Around Christmas, she had read books that prompted summaries related to the holiday. But just before the new year, she finished three books by Black authors.

On Dec. 29, when Ms. Trammell saw her Fable summary, she was stunned. “I thought: ‘This cannot be what I am seeing. I am clearly missing something here,’” she said in an interview on Friday. She shared the summary with fellow book club members and on Fable, where others shared offensive summaries that they, too, had received or seen.

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