The menu module for the the header in the theme builder has a fly in animation that can't be turned of in the module settings.

/*** START disable menu animation ***/
.et_pb_menu_0_tb_header {
animation: none !important;
}
.et_pb_menu_0_tb_header .et-menu a{
transition: none !Important;
}
/*** END disable menu animation ***/
Code language: CSS (css)

Or this one

/* START disable animation on load */
selector .et-menu a {
transition: none !important;
}
/* END disable animation on load */
Code language: CSS (css)