Which players do you think underperform? To me, Van Hecke and Courtois are playing even better. I think teams get used to their style and they are preparing better tactics. Since they are using alsways same 7 players (only Bland is contributing among bench players), it is not hard to get used to their style.
In terms of individual players, I think Leys and Aelbrecht are not contributing as much as they should, but my main concern is the overall team play. Last year they had this "flow" in their game, they were simply "clicking" and I don't see it this year.