A special television crew that put together the Harry Potter cast members received mixed reviews from critics, with much of the absence of writer J. K. Rowling.
There has been speculation that the author was barred from appearing after earlier comments about waria divided public opinion.
Rowling did not appear with the cast in the particular program and can only be seen in archive videos.
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In the film special, former child stars Daniel Radcliffe, Emma Watson, and Rupert Grint reunite with other cast members, including Robbie Coltrane, Helena Bonham Carter, Jason Isaacs, Gary Oldman, and Ralph Fiennes.
However, while some actors like Coltrane mention Rowling in their interviews, Rowling herself has only appeared through videos shot in 2019.
The Times described it as an "interesting if sometimes sweet collection" with "no key ingredient" on Rowling.
"Where was Joan Rowling when we needed her the most?" asked The Telegraph in its two-star review.
The Warner Bros. or HBO writers have not officially confirmed the reason for Rowling's absence.
"If you haven't had enough sugar for Christmas, an overdose of this collection of Harry Potter extravaganza should fix it," wrote Carol Midgley in The Times.
"Back to Hogwarts is a long, lavish festival of nostalgic love, with the main stars queuing up to share memories of filming and of course, to say how much they 'love' each other (there are lots of them)."
However, in the four-star rating that tested positive, Midgley said Rowling's lack of new content was noticeable.
"The fact that Rowling wasn't sitting in the Gryffindor common room or strolling Diagon Alley and the actors who were children at the time admitted what they owed their careers seems like a strange and important omission," he said.
Ed Power of The Telegraph noted that Rowling "appeared in several short videos from 2019" but instead complained about her "absence."
"It's less important," he said. "Even Muggles would conclude that Rowling's lack of time in this documentary has something to do with the public's criticism of the show's stars in response to their views on possessed people."
He said the special was "pretty annoying, with a saccharin, petroleum jelly feel to the lens of a John Lewis Christmas commercial."
"What was missing, in the end, was the real picture of Harry and what has captivated so many readers. And frankly, only Joan Rowling can offer this kind of insight."
