The Black Corsair Elite near the Captain’s Quarters falls into the rocks and cannot be reached.
One time, the Elite fell to the other side of the rocks onto the platform with the two NPCs and cages; I was able to fight there.
Walk out of render range and back.
NPCs falling through the ground has been… well it’s a legacy bug on PC. They have fixed the collision mesh in a few areas, but it’s pretty well a common issue.