Wanted to chime in because a client of mine has run into this issue. There is a problem with the latest version of jQuery (1.12.3) and either this plugin, or another plugin that is causing a downstream issue with twentytwenty.
A quick (but bad) fix can be to revert to an older version of jQuery, 1.11.3 works. But this is a bad solution because it’s swapping out the jQuery that ships with WP Core for an older version. I’d avoid it for any production websites, but it can be a temporary solution while you fix the problem. Because this is a bad solution, I don’t want to link to ways to revert back to jQuery 1.11.3, but you can google it.
A better fix is to investigate what is causing jQuery to not fire on the front end. In the case of my client it is this:
unrecognized expression: a[href*=#]:not([href=#])
And in the case of the user Sequiturs up there, it is similar
Syntax error, unrecognized expression: .mobile_menu > ul > li.has_sub > span.mobile_arrow, .mobile_menu > ul > li.has_sub > h6, .mobile_menu > ul > li.has_sub > a[href*=#]
Sequiturs, if you’re using a mobile_menu plugin you can try disabling it, and then seeing if this twentytwenty plugin works again. That would help isolate the issue.
I’m going to do some more investigating and try to isolate the issue with this plugin against a blank WP install.
Stay tuned.
Cheers.