I find that the Crescent Moon piece always spawns under the floor or not at all - breaking the quest
By opening the player console and by typing player.additem 030117d 1 the Crescent Moon piece item appears in your inventory and can be placed on the Moon Dial and allows the quest to progress. Without it the quest is broken. Reloading Saves made no difference and advancing the quest using setstage didn't help as the dial remains closed.
I hope this is the right place - I'm not sure which board is appropriate. I want to add this as a bug fix on the main Wiki page but have no idea how too. If anyone does please feel free to do so - or let me know and I'll do it. Thanks