Their are many reasons a buck turnes nocturnal. Their are too many factors to consider. I would focus on yourself, take some time to think about it, have you given him a reason to go nocturnal. These guys don't get big for being careless. Maybe you jumped him sometime and didn't know it or maybe your using the wrong entrance or exit when going into the woods? All lot of factors to consider. I'm not saying that your not doing the best you can to get him. But try to eliminate human error as much as possible.