As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PILOT REPORTED THAT WHILE CLIMBING THROUGH FL210 THE THRUST REVERSER UNLOCK ANNUNCIATOR ILLUMINATED. THE FLIGHT CREW PERFORMED THE EMERGENCY STOW CHECKLIST WHILE LEVEL AT FL240 WITH AIRSPEED BELOW 200 KIAS, THE MESSAGE DID NOT EXTINGUISH. FLIGHT CREW RETURNED TO THE AIRPORT AND MADE UNEVENTFUL LANDING. MAINTENANCE FOUND THE RIGHT THRUST REVERSER OUTBOARD STOW SWITCH TO BE INTERMITTENT. THE SWITCH WAS REPLACED AND PASSED ALL OPERATIONAL CHECKS.