Why is the grid only visible through the holes?
Try double-tapping (on iPad) on the face (or select face and enter Sketch) and you will see the grid
Thank you Daniel, but what is the logic behind this? I guess the grid is at the bottom of the body and after tapping on the face the grid comes too the top. Right?
By double tapping on a plane, you can define which plane to sketch on.
Aha! Clear now.