The worst thing a defender can do in a high line is be passive, and that’s Lindelöf’s entire game. Slow defenders like Hummels, Puyol have excelled in high lines because they get tight and win the ball high up. What they don’t do is passively exit the defence with some “half pressure” and allow an attacker to do whatever the hell he likes with a ball. Lindelöf is being instructed to do something which is alien to him, and that’s why we see instances like the 3rd goal at the weekend; what Lindelöf naturally wants to do there is allow the attacker to have the ball and back off, but now he’s being told to get tight and win the ball high, but he can’t.
A lot of fans have got it completely mixed up and think that he’s more suited to a high line because he’s faster on the turn, but when the high line is functioning well, centre backs shouldn’t be getting into constant foot races on the turn, that’s be evidence of it failing.
In short, he’s horrendous in a high line and suits much more what Mourinho wants to do, which is why he bought him.