Agreed, there is a technique component to it. I’m just not sure it’s “110% mental” as the other poster put it. his bat speed went from 10% above average to 4% above average. Meanwhile his fast swing rate went from 3x league average to 2.2x. So his drop isn’t in the max speed, but in the frequency of it.
He’s clearly adjusting his swing, he’s off, but it could be he’s compensating for something physical. Maybe it’s the ribs, maybe it’s his legs, or something else.
It’s very clear that the plane of the bat is inhibiting his ability to square it up. if it was just a mental technique thing, why would his swing get flatter?