I was also having problems with a broken Appearance > Menus screen in the admin after upgrading to WordPress 4.4
While trying to debug the problem, I narrowed it down to The Events Calendar.
Disabling the plugin fixed the Appearance > Menus screen.
I’m using v4.0 of The Events Calendar. Editing menus in the customizer still works fine.
For me not even the Customizer works. But that may be a conflict with another plugin. Disabling The Events Calendar, changing your menu and then re-enabling it seems to do the trick if you need to update your site’s navigation.
I am having the same problem.
After upgrading WP from 4.3.1 to 4.4, The Events Calendar makes the Dashboard -> Appearance -> Menus no longer work.
I hope this can be resolved soon.
everything seems solved with v4.0.1 update, thank you!
