Having rewatched much of the match, Wan-Bissaka's performance is even worse than I thought on first viewing.
Going into the match, Angelino was Leipzig's top scorer in the Bundesliga with 4 goals and joint 2nd best for assists, 3rd for key passes. In the CL he was also their top scorer with 2 goals and had the most assists (2).
So Wan-Bissaka decided to leave him completely free time after time. Leipzig's main tactic was to play the ball wide, normally towards Angelino, though sometimes to the right, as soon as possible.
Angelino scored, got an assist for Haidara's goal, put in the cross that got deflected resulting in their third goal, created their big chance for Forsberg who shot narrowly wide, had another shot from an angle that he didn't get a good connection so an easy save for De Gea.
Then there was the bizarre attempted backheel when Wan-Bissaka got pressed by several Leipzig players, that resulted in Shaw conceding an unnecessary corner, that led to them hitting the post and then the goal that was disallowed for offside.
Unbelievable.