when the communication fails, you hesitate, when you hesitate, you start thinking, and when you start thinking the other team already snaped the ball, you overreact and overpursue. You don't trust your teammate got the play right and you overcompensate for him, taking you out of your assigned position.
You can aid this with a more simpler system, in Schwartz's system, the rookie Preston Brown called the plays, the system worked for everyone. We should look into going to a similar system next year (for the sake of defensive players)
Gilmore, though, as Eball said, lacks fundamentals of how to tackle properly.
in the off-season I posted a video of how the Seahawks hired some rugby coaches to teach them how to tackle. I hope our next HC guy can implement something similiar.