Hey Gal,
The empty is the parent to the cube children,
The children follow the parent wherever the parent goes.
So the empty (parent) is moving (sliding) along the curve, as the follow path constraint intends, and the 6 cubelets follow along.
It looks to me as if everything is working as it should be. When You render your animation, objects such as empties are not visible.
If it is a distraction in the viewport, you can hide the empty in the outliner.
I usually put any utility objects such as empties in a UTILS collection and hide the collection.
