Harry is in is first full season, so surely he's allowed a cock up or two as the lad is still learning, you do hear moans and groans, but that's to be expected. McDonald is probably one of the best passers of the ball in the first team at the moment, and the constant "tossing" the ball away to the oposition has been Monty's job for how ever long, so thats why he will get away with it for now.
Simonsen on the other hand has had a fair few years of football behind him, and some of that at the top level. For him to keep dropping clangers every week, while we shouldn't be constantly on his back, it is not something you'd expect from a goalkeeper of his supposed caliber.