As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) CABIN PRESSURE MASTER WARNING CAME ON AT FL 200. DIFF PRESSURE WAS 4 PSI AND DECREASING & CABIN CLIMBING PASSING 10,500`. INITIATED AN EMERGENCY DECENT, CREW WENT ON OXYGEN AND DESCENDED TO BELOW FL 100. AIR TURN BACK PERFORMED. (TC# 20190531005)