More than likely, nothing.
He posted an absurdly high BABIP of .426 in the 1st half, and he's at .250 for the 2nd half.
Sure there's an adjustment that happens around the league, but it's not like his power was a surprise. Teams were trying to jam him up inside early in the season too. I don't think there's any secret that the league has on him.
I'll just say that he's in a slump and he's been a bit unlucky.
It's ugly, to be sure. His K-rate went up 5% which is probably him pressing a bit. But his BB rate is stable.
He'll be fine.