Mobile Menu disappeared

Hi guys,
We have a question, after we update nextgen gallery plugin to version 2.0 our menu disappeared on mobile devices.
We use the responsive theme version 1.9.3.3 does anybody know how to fix ?
Maybe its something in the css.
Our site is https://www.catwalk-vintage.nl
On the collectie page can you see a nextgen gallery.

Thanks in advantage

https://www.ads-software.com/plugins/nextgen-gallery/