It sounds like an exaggeration but these scenes happen almost every week. In the second goal against Everton we had 3 defenders in that way, so Sigurdsson had an open corridor to shoot.
Against Watford I even wrote a post with pics to show how useless these guys are at reading basic situations in the game. We were playing with the diamond and two forwards, and those defending were hypnotized looking at the ball. The ball is released seconds later to the player coming from behind on the right side and still nobody realizes, so he had the chance to shoot without opposition. Then we have Shaw man marking the other guy while the rest are keeping the line, pure comedy.
https://i.imgur.com/7DioHQO.jpg
https://i.imgur.com/pMhGkal.jpg
https://i.imgur.com/ViqVJNj.png
https://i.imgur.com/5QwZRkz.jpg
https://i.imgur.com/NqSzzh6.jpg
I think this team haven't developed in the last 6 years any kind of ability to defend deep. With LVG it was masked by our long spells on the ball, but we weren't too reliable when we were pushed back. I think Mourinho tried it more than anyone but he wasn't capable, even with 10 men sitting behind the ball we depended on De Gea doing wonders and their strikers missing open chances.
The way I see it we're missing a lot of leadership and communication at the back, starting from the keeper and followed by the centerbacks. They're decent players individually for me, I don't think neither of them is particularly bad and De Gea in normal conditions is top class under the posts, but working as a unit they're a mess.
We're lacking more commanding players in my opinion to anticipate and identify dangerous situations, and fix them just in a pair of seconds. The defensive block looked fine to me while we pressed high under Ole for some time, but once we gassed off after 60-70 minutes all the cracks appeared again, and mainly after the injuries around march we're seeing again the same ghosts from the past.