What was found
DURING FLIGHT, INFORMATION ON LESS PAGE DISAPPEARED. BOTH FMC SCREENS DID NOT GO BLANK BUT LINES 1, 2, 3, 4, DISAPPEARED. NO LESS INFO WAS DEPICTED MEANWHILE BOTH ND'S DISPLAYED CURRENT INFO IE MAGENTA LINE, ACTIVE WAYPOINT, DATA ETC IN AN ATTEMPT TO RESTORE LEGS INFO, TRIED UNSUCCESSFULLY TO INPUT DESTINATION ON BOTH LEGS AND ROUTE PAGES, TRIED TO MODIFY RTE 2 BY ENTERING A WAYPOINT; THE WAYPOINT APPEARED ON RTE 2 PAGE, ALSO ON ROUTE 1 PAGE, ON ROUTE 1 PAGE, EVEN THOUGH WE DIDN'T EXECUTE ON RTE 2 PAGE. ACFT GROUNDED. PERFORMED FMCS BITE PROCEDURE ON LEFT AND RIGHT FMCS IAW FIM 33-61 TASK 801, NO IN FLIGHT FAULTS NOTED FOR THE LAST FLIGHT LEG AND NO SENSOR FAULT NOTED. NO HISTORY OF THIS ISSUE IN THE LAS 90 DAYS. ACFT OK FOR SERVICE.