You are so intent on the deer that you can't seem to get the bow in front of you correctly. It's like you can't let the bow get in the way of your view.
Does that sound familiar at all? It's just nervous anxiety when you are drawing on that deer then. If this is what's happening then you just need to close your eyes for a second and draw with good form. If you do it the same as in practice, that peep will line up for you. Summing it up, your drawing differently when your target is a deer.