Mobile menu "jumps"

Hey there!

Webpage is blomstra.de/about

The menu does some weird things on mobile & tablet.
On desktop it nicely sticks to the top and changes size very smoothly:

Yet on mobile, it somehow jumps when scrolling down:

Any idea what could have caused this odd behaviour on mobile and how to fix it?

Thank you very much & all the best,
Daniel

Might have to do something with this custom CSS code to enable sticky menu on mobile, which I picked up from another help topic:

  @media only screen and (max-width: 1024px) {
      .site .site-header.fixed.float-header {
        position: fixed !important;
      }
    }

Try adding this code to Appearance > Customize > Additional CSS from dashboard.

    @media only screen and (max-width: 1024px) {
      .site .site-header,
      .site .site-header.fixed {
        position: absolute !important;
      }
      .site .site-header.fixed.float-header {
        position: fixed !important;
      }
    }

Regards,
Kharis