The United players look a bit like damaged goods. Mentally vulnerable.
It has stroken me in many matches how badly United respond to conceding goals. In the period following a goal against, United are always on their heels. I think it´s been like that all the time under Solskjær, actually, but you have most often gotten away with it, and even come back in the end of games. Like against PGS, but after they scored, United were lucky not to concede another one and mid first half was a real nightmare. Wolves scored pretty much first time they crossed the mid circle, and all domination was suddenly gone. The top teams would have kept the domination, and maybe even stepped it up.
Damaged goods. That´s also maybe why United struggle at home with all the scary fans.