As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
L PACK LIGHT ULLUMINATED AT LEVEL FLIGHT. FL350. ACCOMPLISHED QRH PROCEDURE, PACK LIGHT REMAINED ILLUMINATED. GROUNDED - YES. FOUND MX MESSAGE 21.55100-21-55030. RESET PER B737-9 FIM 21-51-00-810-807. MESSAGE CLEARED AND LH PACK REMAINS EXTINGUISHED.