Okay for everyone doing harvest princess, here's what you need to know
This quest was kinda fuckin weird to do because the order of operations. In order to get the bell you have to do this whole process of going back and forth between day and night because of how its all mapped in the game. You first get the quest from talking to the princess at day time (after gaining access from the reign) and she'll ask you to look for her bell. After you get the quest you have to wait until night, use sleep powder to break into the "throne room" and go into the basement to find the windmill key and begin your investigation.
This is where I imagine most people fuck up because they go to the windmill immediately. This makes perfect sense. The problem is you're supposed to follow the trail of flour to the bags in front of the entrance and examine them and then follow the flour trail back downstairs and look at the table that the bell was on where you got the windmill key and sir knight deduces that someone hid in the flour sack and waited for the right time to get out and steal the bell. You have to do it in this order or you don't trigger the events properly and cant proceed. And for those who went to the windmill first, you can turn the windmill off and after a few days the flour reserves in town dwindles because the windmill isnt making any. You can then take the egg and the chest (with the rotting cornucopia) and then turn the windmill back on if you want.
After you trigger those events in the harvest princess' house you can pretty much continue the quest as you normally would have without the pointless investigation. Although in my opinion the windmill key should have been left in the flour sack OR you should have gotten it the second time you investigate the basement because getting it right away kind of throws you off since your first instinct is to immediately go where it points, which is the windmill. From there the rest of the quest is pretty simple to follow. It just becomes tedious when you have to constantly rest and go from day to night since theres two halves to this quest line and it has to be night to access part of it.