A 28-year-old male with a family history of malignant hyperthermia undergoes elective knee arthroscopy under general anesthesia. Fifteen minutes after induction with propofol and intubation with rocuronium, the anesthesiologist notices a sudden rise in end-tidal CO₂ (ETCO₂) from 35 to 65 mmHg, muscle rigidity, and tachycardia (HR 140/min). Which of the following is the most common cause of this acute perioperative crisis?