Responsive Menu not working all the time

Hi, The responsive menu on my blog-website robertfairhead.com has stopped working reliably all the time. I first noticed the problem when I tried to upgrade my Catch Box Pro theme from 4.6.9 to 4.9.1. As there were a number of other issues with the upgrade, including losing my Custom CSS settings, I decided to roll back to 4.6.9, but the responsive menu problem has continued. If I click on the three horizontal bars, nothing happens. I've tried it on Safari on a Mac, Mozilla, and Safari on my iPhone. Refreshing the screen sometimes works, but more often not. When I debugged the script I found this error message in catchbox.slider.js: jQuery(window).load(function() { Can't find variable: jQuery ... } I have tried deactivating recently installed plugins, including Wordfence. But this hasn't helped. I've also taken out script for the Twitter and Facebook plug-ins, but again this has made no difference. Do you need to log into my website admin area to investigate the cause of the problem? This problem has had me stumped for 1 1/2 days and I sincerely hope you know the cause and have a solution! :) Regards, Robertf