When scrolling on a mobile device if you use the navigation and accidentally scroll the page instead of the navigation the navigation turns on all white hiding the text when you click the navigation again.
This is difficult to explain so let me break it into steps.
Click mobile nav toggle
Toggle a dropdown menu item so it expands
Scroll on the page while leaving the navigation open
Tap the navigation to scroll
This sounds like it wouldn’t happen often but I experience it several times.