In the Boost theme, clicking the button at the top left of the screen will enable/disable the navigation drawer by sliding in/out. If this button is pressed two times in quick succession, that is to say, two times before the animation completes, then the contents of the navigation drawer will disappear.

The easiest way to replicate this is to be on a Moodle page with the navigation drawer enabled and then double click the activation button.

The problem can be observed by inspecting the page and examining where the contents of the navigation drawer are still set with 'display: none'.