As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER TAKEOFF THE CREW RETRACTED THE LANDING GEAR AND RECEIVED A LANDING GEAR DISAGREE EICAS MESSAGE. THE LEFT MAIN GEAR WAS NOT INDICATING RETRACTED. THE QRH WAS FOLLOWED AND THE GEAR WAS CYCLED AND CONTINUED TO INDICATE THAT IT WAS NOT RETRACTED. THE AIRCRAFT RETURNED TO STL AND LANDED WITHOUT INCIDENT. MAINTENANCE CHECKED THE CMC FOR RELATED MESSAGES WITH NONE PRESENT. THE PROX SWITCH CONNECTORS WERE REMOVED, CLEANED, AND RECONNECTED WITH NO FURTHER DEFECTS NOTED.