When the film was shown in Iceland, which uses subtitles rather than dialog dubbing for films with non-Icelandic languages, Jason Momoa's pronunciation of his single line of Icelandic was so unintelligible that it had to be subtitled into Icelandic (often resulting in audience laughter).
Director Zack Snyder and his wife, producer Deborah Snyder, stepped down from finishing the film after the suicide of their daughter in March 2017. They tried to remain involved in the film as a way to work through the difficulty, but after two months decided to step away from the project to spend time with their family. Joss Whedon, who had signed on for Batgirl, took over as director, managing additional scenes that need to be included in the final cut. Warner Bros. stated that Whedon would direct and write in the same style as Snyder so there won't be any tonal shifts or obvious changes in style. However, Whedon controversially fired Snyder's composer, Tom Holkenborg, and replaced him with Danny Elfman, who previously composed Whedon's Avengers: Age of Ultron (2015). Nevertheless, in 2021, Snyder was able to show the movie the way he originally intended it.
Extensive reshoots in London and Los Angeles in mid-2017 added a cost of approximately $25 million to the film's budget. Henry Cavill worked on the reshoots and Mission: Impossible - Fallout (2018) at the same time. He had to sport a moustache for his role in the latter project. However, Paramount refused to let the actor shave it off to play Superman in the reshoots. This meant that Cavill's facial hair had to be digitally removed in post-production. However, due to a tight schedule, the results were crude and were among the many criticisms of the theatrical version of the film.
Holt McCallany, who plays the burglar in the first scene with Batman, said the scene was written and shot by Joss Whedon as comedic, but Warner Bros. preferred to open the film with a more serious tone, and the scene was re-edited. When McCallany returned home to New York, he found a bottle of his favorite champagne at his door and a note from Whedon that said, 'To battles lost. Gratefully, Joss.' McCallany appreciated Whedon's gesture and had the letter framed.
Some of the gods seen defending Earth from invasion are Zeus, Ares and Artemis.