I don't want to over-analyze his game, I just want to make one observation:
I noticed something physically wrong with him after the All-Star break. He had no elevation, and he ran down the court like he was running on a turf of spikes.
I've been suspecting something ailing him and he didn't disclose it to the public. It's not the first time he's done this; he injured his hand previously and went through a bad slump and then during the off-season disclosed he had been playing through a hand injury, he couldn't feel his hand or something... which MIGHT have a slight impact on your shot, I dunno, just a hunch.
I suspect that a large part of his poor play was something physical with him... feet... back.... something... I would not be shocked at all if it came out that he's having feet problems, guys his size typically struggle with that.