As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
JFK INFLIGHT T0635/21, YELLOW SYSTEM HYDRAULIC WENT TO 50 PSI SHORTLY AFTER TAKEOFF WITH ECAM MESSAGE. SYSTEM WENT TO 3300 PSI AFTER PTU PRESSED ON. RETURNED TO JFK. LANDED WITHOUT INCIDENT. REPLACED RIGHT HAND ENGINE YELLOW SYSTEM PUMP. SYSTEM GROUND CHECKED NORMAL OPERATION.