Thanks buddy!
About the demons disappearing, it's not a bug, demons will teleport back to their original positions when player leaves from their sight for a period of time. The length of time may be slightly shorter now, and it will be adjusted later based on feedback. Did you remember where they shoot you through walls? I would check it.
About the dead-ends, maybe I should place some faint light at the dead-ends.
About the keys, did you mean need some storytelling or addiction ability when you get a key? ( sorry my suck English). But it reminded me maybe I should add a msg sort of 'Got a red keycard' when player got them.
Thanks again about the feedback my friend! I will keep pushing Hell Hunt getting better:)