As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PASSING THROUGH 21,000' POPPING NOISE HEARD AND THEN LOUD NOISE OF RUSHING AIR FROM ESCAPE HATCH. RETURNED TO DEPARTURE. GROUND CHECKED REVEALED OVERHEAD ESCAPE HATCH NOT FULLY CLOSED. VISUALLY CHECKED AREA, ALL OK AND PERFORMED OPS CHECK AND DOOR CLOSED IAW MM 52-21-00, ALL NORMAL.