As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: PILOT REPORTS AT FL 350 THE CABIN RATE OF CLIMB STARTED CLIMBING AND DESCENDING 500FT PER MIN. THRUST LEVERS WERE NOT MOVING. SAME THING AT FL 290. MAINTENANCE REMOVED AND REPLACED CABIN RATE OF CLIMB INDICATOR IAW AMM 21-33-01.