The common denominator here of course being Maureen. Great players, good players, and even so-so players suddenly become dreadful under his tutelage. Lukaku is not and never will be a top player: he'd have been far better off under Pulis or Fat Sam because they would use him for what he does do - become a battering ram.
Up until recently Sanchez was scoring for fun. He seemed to be enjoying his football, he was expressing himself and both making and taking chances. But predictably enough, Maureen wants him to shore up the defence.
It's an absolute litany of player failing at the swamp, but it's not because they have bad players (aside from a couple I can immediately think of), it's down to bad management.