Don't think it's baffling at all really.
To me, Haji's loss of form is just a double whammy of the team performing worse as a whole, so we're creating less chances, and he has missed a few chances, so his confidence is on the floor. I really think it would pick up again with a goal or two (and he's been quite unlucky not to get one, disallowed goal at Preston, multiple pens not given, inches away at Stoke etc.).
I don't really get the vitriol directed at him for it because as of right now it is the exception, not the rule.