What happened to Gwen Stefani? On Saturday, August 10, the rock star, 54, shared an Instagram Story revealing that she was canceling her upcoming concert due to a medical issue. “As a result of a recent injury and in consultation with my doctors, I’ve been advised that I’m not able to perform on August 17 at Hard Rock Live at Etess Arena in Atlantic City,” the Grammy winner shared. The mother-of-three did not include details of what caused the injury. “I’m so sorry and we are planning to reschedule the show as soon as possible,” Stefani added noting fans will know “as soon as the new show is a…