Is it possible that the arrow drove right through the deer?
In bowhunting, a clean arrow means a clean miss. As for missing, there can be a myriad of reasons when using a bow from a treestand. The angles presented when shooting from a treestand and your position when taking the shot are a couple. So is the wearing of clothing that may have inadvertently hit your string or made for a slightly different anchor point. A small unseen branch or twig or just excitement. The chance of missing is why it's called hunting. The increased chance of missing is what differentiates bow hunting from gun hunting. If we never missed or went home empty handed, there would be no challenge and no reason to be that proud that we mount the head and put it on our wall. Be happy you missed clean and that you or someone else still has the chance to hunt and take the animal, instead of a poor shot leading to a long and painful death and a lost animal.