As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CRUISE FLIGHT CAPTAIN'S NAV DISPLAY SHOWED VTK FLAG AND BOTH MCDU'S REVERTED TO THE MENU PAGE WITH A MISSING FMC PROMPT. AFTER ABOUT 15 - 20 SECONDS NORMAL OPS WERE RESTORED (VTK FLAG WENT AWAY AND FMC PROMPT WAS RESTORED. GROUNDED - YES. ACCOMPLISHED FIM 34-61 TASK 836. DETERMINED TO BE AN INTERMITTENT FAULT. RESET CHECKED OKAY. OPS CK NORMAL.