If you’re using the Underscores theme (also knows as _s) by Automattic, you may have tried to add multiple menus to the page and been frustrated when they don’t work on mobile.
Here’s a bit of Javascript to add to the theme’s navigation.js file to fix the issue:
https://gist.github.com/macbookandrew/74fd6dd1d101debcf6890778052609d4
Hmm, thanks…you say add it to the existing navigation.js? Where? At the bottom of the existing file?
It’s been a very long time since I looked at this, but that sounds about right.