Ok, I'll tell you something weird I've been noticing. It's not that they're not running, but they're running to no purpose, and sometimes to disastrous purpose.
Look back at the highlights of the United match. United winger overlapping, he's up against Walker. Walker's jockeying him, slowing him up, doing his job as a full back in fact. About ten to fifteen yards away is Bernardo. Now Bernardo's man, a few yards away from him, is Fernandes. Suddenly Bernardo takes it into his head to race over to back up Walker (who doesn't actually need him at that point). Winger sees it, puts the back inside to a now perfectly free Fernandes. He puts the ball inside to the one skilful player still left in that team, he's got all the time he needs to tee it up, and to be fair, he duly puts over a perfect cross right to the head of a United player in the box. Watch any recent game, slow it, pause it, and you'll see that this kind of thing has been happening a lot. It's as if they don't trust each other any more, even as if they don't know each other any more.