Well it's very clear his swing decisions are pretty much total crap. As for what's causing that issue, that's anyone's guess. It's like he wants to hit everything, or...he is getting fooled a ton because he's guessing and guessing wrong alot. He's late on fastballs all the time.
My untrained eye and speculation is that hes so focused on not getting beat with breaking balls low and away that he's sitting soft and getting beat by fastballs as a result. It's somewhat understandable given that pitchers feed him a steady stream of offspeed pitches more often than not, so he's trying to prove he can hit them rather than being ready for the fastball and adjusting to the offspeed.
Then there's the PAs where you can tell he's sitting dead-red and just waves at changeups all over the place.
Teams may have a pretty good tell on Vlad after analyzing video on him that shows if they throw him a certain pitch in a certain location, they have a good idea at what he's likely to do next. Like they're coaching the pitchers to exploit his mental patterns.
A possible example of this is...whenever the pitcher gets a strike close call on the outer edge, if they can execute a similar pitch another 3-6 inches further out, he will be swinging at it,which is exactly what they want him swinging at. That's one pattern I've noticed a ton.