Cannot Focus on Object Closer than 533 Pixels

You could also try playing around with the camera's Focus Distance to focus on a specific object based on its focal length. It is useful for any element that is a 3D Layer and when you have the Depth of Field enabled in the camera. Look at the screenshots that I leave you, I hope they will help you.

If you have camera wireframes visible and you set up your multiple views, you can see the plane of focus interacting with the other layers. 

Another option is to use vector math to measure the distance between the layers and that will guarantee focus on the anchor point of a layer. As long as the Camera's point of interest is pointed right at the anchor point of the target layer this expression should keep things in focus as long as the layer is a vector layer.

point1 = position;
point2 = thisComp.layer("Target Layer").position;
length(point1, point2)

Moving the camera closer to the camera than the zoom value will scale up footage and images to the point that it looks out of focus. It looks to me like your layer is made up of pixels because it is a nested comp and collapse transformations are not turned on and you made it 3D, so I'm not surprised that it is going soft. 

This is not a bug, it is incorrect user expectations and/or workflow.