Mobile menu in theme north not working

The mobile menu doesn’t work for me (tested in Firefox on desktop and in Chrome on Samsung mobile).
Only the animation is visible (Hamburger to checkmark)

North 1.2.5 and WordPress 4.6.1
Plugins: siteorigin css, pagebuilder, black studio

As I like North much, especially the clever theme setup, I tried a workaround to set the mobile breakpoint to a low value (e.g. 100)
That didn’t work, either.

Is there a way to completely disable the mobile menu, because I only have a simple menu that fits on mobiles?

Would an upgrade to pro version help?

Regards

Norbert