As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
NR 2 FMS AND SBAS NR 2 FAIL CAUTIONS. PERFORMED AN AIR TURN BACK DUE TO LACK OF VISIBILITY TO CONDUCT SINGLE FMS APPROACH. C/W FMS OPERATIONAL TEST IAW MTC 6346104. NO DEFECTS NOTED, NO FAIL/FAULT MESSAGES OCCURRED. RETURNED TO SERVICE. COULD NOT DUPLICATE. NO PARTS REPLACED.