Option A is incorrect. 'misfunctional' is not a correct word. Thus, it cannot be the answer.
Option B is incorrect. 'disfunctional' is also not a correct word. Thus, it does not fit in the blank either.
Option C is incorrect. 'dysfunctional' means 'impaired in function.' Although it has a meaning that is close to that of the required one, it is generally used to refer to living beings or bodily organs. Thus, it is not the best fit.
Option D is correct. 'Malfunction' means 'cease to function properly'. It is used to refer to machinery or equipment. Thus, it has the required meaning and is the correct answer.