The Salt Path star Gillian Anderson has said allegations that the memoir was fabricated felt like "a betrayal" after spending time with the couple.
Anderson played Raynor Winn in the film adaptation of the 2018 memoir, which was released in the UK last year.
It tells the story of how Winn and her husband Moth, who was diagnosed with a neurological condition, walked the South West Coast Path after losing their Welsh home.
But an investigation by the Observer suggested some of Winn's claims about the events that had led to the couple losing their home had been misrepresented.
Winn previously described the Observer's article as "highly misleading" and said the couple had been taking legal advice.
The book and its film adaptation depict a couple who decide to walk the 630-mile (1,013km) route after their home was repossessed following a bad business deal.
But the Observer reported that Winn - whose legal name is Sally Walker - and her husband, Moth Winn, had lost their home after she had taken out a loan to repay money she had been accused of stealing from her previous employer, Martin Hemmings, an estate agent and property surveyor from north Wales.
In a statement issued last year, Winn said she stood by the book's description of how they came to lose their house, saying the dispute with the Hemmings did not result in her and her husband losing their home.
The Salt Path film will be released across the United States in September by Rialto Distribution.
Anderson, who plays Winn, and Jason Isaacs, who plays Moth, have spoken about the controversy that clouded its UK release for the first time.
She described the situation as "really disappointing" in an interview with the Times after spending time with the Winns.
"We had been so surprised by its success: 'What, really, this film about two old people going on a walk?' It felt like such a betrayal because we'd spent time with [the Winns]," she told the newspaper.
The Times said she had not heard from the couple since.
Speaking to Radio Times, Anderson said it was "very unfortunate" as the film was "doing really well in the UK - beyond my expectations".
"I think we were about to sign with Sony Classics for the United States the week when the article came out, so it sucked, and continues to suck."
She said that she had hoped audiences would be able to experience the film "as its own entity" regardless of the controversy.
Earlier this month, Isaacs said that doing publicity for The Salt Path's US release was "going to be interesting" while speaking on the Kermode On Film podcast.
He added: "I said, 'Are you sure you want us to do publicity?' They went, 'Absolutely.'"
The actor, who played Lucius Malfoy in the Harry Potter film series, said he supported the decision as it was a "beautiful film" and "much of it is still completely valid".
He added: "Obviously, some of the things have been questioned. It's going to be an interesting experience."
The Observer said that it had also spoken to medical experts who were sceptical about Moth having corticobasal degeneration (CBD), given his lack of acute symptoms and his apparent ability to reverse them.
In July 2025, Winn posted clinic letters on Instagram addressed to Timothy Walker, Moth's legal name, which she said showed that "he is treated" for CBD "and has been for many years".
In a statement at the time, she said: "The Salt Path is about what happened to Moth and me, after we lost our home and found ourselves homeless on the headlands of the south west.
"It's not about every event or moment in our lives, but rather about a capsule of time when our lives moved from a place of complete despair to a place of hope."
At the time of the Observer investigation, publishing house Penguin said it "undertook all the necessary pre-publication due diligence", including a contract with an author warranty about factual accuracy, and a legal read.
It added: "Prior to the Observer enquiry, we had not received any concerns about the book's content."
The Salt Path was originally set to be released in the US and Canada on 22 May, but has been pushed back to 4 September.
Winn had been due to release another book, her fourth non-fiction title, On Winter Hill, in October 2025, but its publication was delayed to January 2028 after the author suffered "considerable distress", according to Penguin.
