Hello:
I recall having this same issue with another site where I use Helix Ultimate.
The corrective action recommended was to add the following to custom CSS:
body.ltr .offcanvas-menu .offcanvas-inner ul.menu > li.menu-parent > .nav-header > .menu-toggler {
right: 0px !important;
}
I went ahead and added the same to the custom css of this site and it seems to have fixed the issue so that the sub-menus now exand out.
I am not really certain why, when I am only using articles and helix ultimate, I am having to add custom css to make the hamburger / off-canvas menu display properly. Seems this shoudl be corrected within helix ultimate itself so the menu works right.
Thank you.
Malcolm