There is a major design flaw with this unit. In fact, it can even be seen in the stock photo. See the gap between the moving bar and the wall base? There is a screw that becomes loose over time (a week) on the bottom of the left wall base. This causes a small distance between the wall and the unit causing that cap. As such, the moving part will fall off the 'notch' eventually and it needs to be re-tightened. Keep an allen wrench handy.
— Mica