As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AT CRUISE FOS CDU WENT BLANK FOR 10 SEC THEN DISPLAYED THE MENU PAGE WITHOUT THE ACARS PROMPT. ON SCRATCH PAD "NO COMM" ACARS PROMPT THEN DISPLAYED ON MENU. OFF & OUT TIMES WERE ERASED. GROUNDED - YES. ACCOMPLISHED B737-900 FIM 34-61 TASK 804 RESET CBS FOR MCDU ON GROUND VERIFICATION. OPS CHECKED NORMAL