Go to this demo https://www.patternfly.org/components/navigation/react-demos/horizontal-nav/

2 ways to show what looks like the same bug:

• load the demo a wide screen where the scrollbars do not show because the nav doesn't overflow
• shrink the page until the horizontal nav overflows
• note that the scrollbars do not show
• they'll show if do something to scroll in that container like
  • move your mouse there and scroll horizontally
  • tab/focus one of the nav elements and use the left/right arrows to scroll horizontally

and the inverse

• load on a narrow screen where the nav overflows and the scrollbars show
• make the window wider until there is no more overflow
• note that the scrollbars do not hide
• the only way I can figure out how to get the scrollbars to hide is by clicking on one, then they'll disappear.

cc @andrew-ronaldson