Perhaps it is me over-reading or over-analyzing things from a mental stand point with the passing to Sane thing but I don't think so. Not only De Bruyne but also Aguero (First half against Huddersfield at home being an example) and even Yaya don't link up enough with Sane . Little things but it can make a big difference. The coordination and understanding between these players and Sane is not there yet but it should improve in time. And thus Sane's game seems to be affected without Silva and/or Sterling on the pitch.
De Bruyne issue is completely mental or psychological. Obviously no one will question his footballing abilities but he has to be mentally consistent. When he went down and stayed down with his head on the pitch after he attempted that pass, It was quite worrying because you think if his mind is suffering for whatever reason then his body will cry out and the risk of injury is higher, which is why that ankle incident was more worrying than usual.
In footballing terms it could be that he has not fully accepted this new deeper role with more defensive responsibilities or is easily fatigued because of it, after all he was very effective when he was moved to the right in the second half. There is also this false idea of interchangeability between De Bruyne and Silva as I think they are completely different players and people may assess his performance in comparison to Silva which is wrong. I don't buy the personal issues like family as he is not the only one with a newborn (Sterling) and he has to be judged as a professional.
Whatever is the issue, he needs to become tuned on mentally for the rest of the season because we need him at his best. But his quality on the ball especially on set pieces or crosses will almost guarantee chances/goals regardless of how well he is performing or how mentally strong he is.