As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) AIR TURN BACK PERFORMED DUE TO UNCONTROLLABLE RATE OF CABIN CLIMB/DESCENT. NO FAULT CODES FOUND. MULTIPLE COMPONENTS WERE REPLACED (CABIN PRESSURE CONTROLLER, CABIN PRESSURE CONTROL PANEL, CABIN INDICATION MODULE & OUTFLOW VALVE). AIRCRAFT IS NOW BACK INTO SERVICE. (TC# 20190618003)