Rachel Zegler, 24, returned to her role in “Evita” on Friday, July 25, after abruptly leaving the London Palladium one day earlier due to a mystery illness.

During the July 24 performance of Andrew Lloyd Webber ’s Evita at the London Palladium, the 24-year-old—who stars as the late Eva Perón in the musical—made a sudden exit from the stage without returni...