It's not really that Andre's chin is bad, but rather that he is 1) horribly predictable and 2) cannot shake old habits.
Andre always leaves his hands down after throwing strikes and always backs away from pressure in a straight line. If anyone puts and pressure on him he completely crumbles mentally. His chin is still good but he has just failed to learn anything from his last four bouts.
I agree. He stiffens up and stays in range w/o any lateral movement, counter punching, or tucking his chin - he's just asking to get tagged and his opponents oblige...anyone who does that is going to get clipped and is going down.