OK, so if it works with site back at Circumference, save all your child theme changes somewhere safe (CSS and other code and files). Then reactivate your child theme and see if the mobile menu shows up still. In other words, the parent theme is apparently working for you, then switch back to the child theme, remove your modifications so you have a blank child theme, then see if your menu shows. If so, now slowly begin to redo your modifications and keep checking the menu. Once it collapses and not seen, then you can pinpoint what was conflicting.