As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AT CRUISE FO HAD VTRK DISPLAYED ON ND DISPLAY AND AUTOPILOT REVERTED TO CWS ROLL MODE. VTRK WENT AWAY AND OPS WENT BACK TO NORMAL. GROUNDED - YES. VERIFIED FMC+DFCS FAULTS FOR FMC DATA INVALID AND PRES POS LAT RATE. NO OTHER OCCURRENCES PREVIOUS FLT LEGS. DFCS BITE, FMC BITE CHKS GOOD REF B737-800 FIMS 22-11-801 & 34-61-801. VERIFIED ADIRU-L AND -R BITE CHKS GOOD AND NO FAULTS REF FIM 34-21-801.