Same happened to me, I didn't attach the body parts and eventually the lights went out and I had a arm in my hand, with no flashlight (flashlight wasn't working because I was no longer holding the gun). There was only a couple of sources of light in the distance (the lit up train notification led for example), the pause button stopped working, I was struggling to progress so had to quit the game. Hopefully gets patched before steam release.
Great demo, really impressed by the realism. I watched the full play through via Fooster on Youtube (random video recommendation), and was glued to the end. I had to download it. I've just been playing resident evil 3 and alan wake, so I had to try this, and it is on a whole new level of horror. Can't wait to see more!
Performance wise : I'm able to get average of 60 fps with this setup :
Ryzen 5800x3d, rtx 4080, 32gb ram, dlss enabled in game, 2560 x 1440, 100% scaling, max graphics.