As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
THREE HOURS AND TWENTY MINUTES INTO FLIGHT AT FL430, LEFT ENGINE N1 ROLLED BACK TO 60% WITH RAPID POPPING SOUND. ITT ROSE APPROX 50C. START WAS DISPLAYED. EPISODE LASTED 10 -15 SECONDS. REST OF FLIGHT WAS FLOWN AT FL400 WITH NO FURTHER ISSUES. REMOVED AND REPLACED THE LT ENGINE.