As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
INITIALLY INSPECTED AND TESTED MAGNETO PRIOR TO INSTALLATION, TESTS WERE SATISFACTORY. A GROUND RUN OF THE ENGINE AND MAGNETO OPERATION WAS ALSO SATISFACTORY. FAILURE OF MAGNETO OCCURRED APPROX 20 MINUTES INTO FLIGHT. ON INSPECTING THE MAGNETO AFTER REMOVAL, FOUND THE MAGNETO POINTS WERE NOT GROUNDING TO THE MAGNETO CASE.