As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING FLIGHT AT CRUISE AT 35000 FEET, VTK ILLUMINATED ON BOTH NAV DISPLAYS AND FMC DISAPPEAR FROM BOTH 'CDU'S. BOTH FLIGHT DIRECTORS DISAPPEARED. PROBLEM RESOLVED ITSELF IN 2 MINUTES WITH NO PILOT ACTION. EVENT REPEATED AND RESOLVED IN THE SAME MANNER 40 MINUTES LATER. REMAINDER OF FLIGHT FMC OPERATED NORMALLY. GROUNDED - YES. PERFORMED FIM 34-61 TASK 836. BOTH FMC'S OPS CHECK NORMAL. A/C OK FOR SERVICE.