Just for anyone else trying to figure out what's up with the locked gate in Vela's underground dance area, I opened the files for the game and there seems to be nothing behind it at all. Like those stairs go to nowhere. I think the dev purposely then put the second gate behind it which will never budge, so that even if you were able to get through the bugged gate, you'd still not reach the steps. Not great, but the rest of the game is pretty well done. Just consider that door and its key as unfinished content.