I’m seeing this issue on two sites:
On my main site: https://www.consolemad.co.uk/ when you start to scroll the page, there is a slight jump in the top bar. It’s most noticeable when using the mouse wheel to scroll down the page. This site is just using the standard theme header with fixed-top. I’m seeing this in Chrome - Firefox is fine.
On a site I’m currently building, I’m seeing the same issue with a custom header that is set to sticky. Unfortunately I can’t link to this site just now. I did try this fix which is a modified version of something I saw on an old forum post:
display: block !important;
this sorts the flickering bar out, but then the main page content starts at the wrong place.
Any advice would be appreciated.