Final answer:
Costume malfunctions are less likely a problem encountered during filming due to the expertise of costume crews and the design of costumes for quick changes, making it the correct answer to the question.
Step-by-step explanation:
The question refers to the problems encountered by the film crew in the fictional movie 'The Dueling Cavalier.' Examining each option closely, we know that lighting issues, sound problems, and script changes are common challenges faced during film production. Specifically, lighting and sound problems are often addressed with the use of special effects or technical adjustments. Script changes are also a part of the filmmaking process, as they can be dictated by various factors, including the vision of the director or changes in the storyline. However, costume malfunctions, while possible, are typically managed by a trained costume crew and the construction of the costumes themselves, which are designed for quick changes with features like Velcro for fastening instead of buttons.
Given the context, and considering the options presented, it is the costume malfunctions that are less likely to be a problem encountered during the filming of 'The Dueling Cavalier' due to the expertise of the costume crew and the design of the costumes to facilitate quick changes. Therefore, the correct answer to the question is: 3) Costume malfunctions.