Hi,
To be honest the problem was made by your custom changes, I mean when you added background image for header, and then dark [=] (mobile menu icon) is not visible (low contrast). You have two solutions:
- Change color of [=] icon or
- Hide bg image on mobile view.
If (1) use that Custom CSS
@media screen and (max-width: 860px) {
#offcanvas-toggler {line-height: 60px;}
#offcanvas-toggler > i {color: yellow;font-size: 26px;}
}
Effect after using it (mock-up)

If (2) use that Custom CSS:
@media screen and (max-width: 860px) {
#sp-header {background-image: none !important; height: 60px;}
#offcanvas-toggler {line-height: 60px;}
}
Effect after

Later remember to disable extra Menu module, now you have two menus there.
