As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
MOMENTARY VTK FLAG ON CAPTAINS ND WITH LOSS OF LNAV/VNAV, THEN RESET ITSELF. GROUNDED - YES. NO VTK FLAG NOTED AT THIS TIME & NOTED RECOVERY OF SYSTEM & VTK EXTINGUISHED. CREW NOTED F/OS NAV DISPLAY SHOWED NO FLAG. CONSIDERED NUISANCE ERROR REF B737-800 AMM 34-61-00. NO HISTORY 30 DAYS & CREW NOTED THERE WAS NO SOURCE SELECT SWITCHING ACCOMPLISHED.