Very odd. This has happened each time? Once you return to third person, you should just be able to see the corpse and interact with it to get a key and unlock the door.
There's another character later in the demo who I noticed didn't spawn one time, but I couldn't repro it and I'm curious if there's something else going on in the 3D side of things that's happening here (and if so another reason to not be using it for a full game lol)