I checked my custom.css file and found that I had removed the code.
I went back in and inserted this into the custom.css file at /templates/shaper_helixultimate/css/custom.css
/* ========================================================================
Shrink Navebar on scroll for Helix Ultimate
========================================================================== */
#sp-header.header-sticky {height: 65px; background: rgba(255,255,255,0.8);}
#sp-header.header-sticky .sp-megamenu-parent > li > a,
#sp-header.header-sticky .sp-megamenu-parent > li > span
{line-height: 65px;}
/* ========================================================================
Shrink logo on scroll for Helix Ultimate
========================================================================== */
#sp-header.header-sticky .logo {height: 65px;}
Now I get resizing again, but the page now scrolls over the navbar, and I lost the smooth animation of the sticky header. Please see hidden content for login details.