There's all kinds of stories floating about out there at the moment but one thing I read, which made some sense, was the loss of Heitinga. The suggestion being that he was the guy who kept the players sweet and allowed Slot to be more removed. We had a wobble under Rafa when Pako Ayesteran left, and that was probably something similar as Rafa was a notoriously poor man manager.
I remembered reading something similar about Sven when he was in charge of England, and the suggestion was that Sammy Lee and Steve McClaren (good coaches, not good managers) basically acted as "middle management", absorbing all the whinging from both Sven and the players, filtering out anything that wasn't going to help. They were supposedly really popular with the players and allowed Sven to function without having to deal with the all the peripheral shit. They allowed the players to have their voices heard without Sven having to hear something he'd have then held against them.
So I wonder if there is something in that, as a lot of the problem at present seems to be a disjointedness between the players and the manager, which is probably putting more pressure on Virgil to act as the middle man, which in turn is affecting his form.
It's not an excuse for the current situation, but it may be a factor.