Robert's scouting report probably says something to the effect of "fastball 6 inches off the corner, sinker, or slider, because he will swing at anything even remotely close to the zone and either strike out or harmlessly pop up"
It's still far too early to actually be worried about him because he's shown off-the-charts ability, but he clearly hasn't adjusted to the league yet and he is not able to simply dominate with his physical ability anymore like he could in the minors.