I upgraded an existing site (a dev version). The header is set to sticky. When I scroll the class .x-bar-fixed is added to the .x-bar.
I use this class to add custom css to the bar. The bar is also set to shrink.
When you scroll back to the top the .x-bar-fixed class is not removed. This means the bar is still smaller than it should be and the custom css does not work.
If I click on a menu item or similar then everything jumps as the class is then removed.