As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) MAIN GEAR UNSAFE APPEARED ON MFDS AFTER GEAR RETRACTION. AIRCRAFT LANDED BACK TO DEPARTURE AIRPORT. MAINTENANCE FOUND THE LANDING HYDRAULIC TEST VALVE LT IN (GROUND ONLY) POSITION. THE VALVE WAS LEFT IN THAT POSITION FOLLOWING A GEAR RETRACTION/EXTENSION TEST AND WAS OMITTED TO BE RE-POSITIONED TO NORMAL. THE (GROUND ONLY) POSITION RESTRICTS THE HYDRAULIC FLOW FOR A SAFE GROUND OPERATION.