I just ran into the same problem, and the same fix worked.
The problem was that $ was undefined (jQuery was still loaded normally), and so that was breaking part of jquery.ui.widget (when $.extend was called). Not quite sure how $ was ending up undefined.
Note: $ is still undefined after disabling Shortcode Embed. So while the issue of $.extend being called is eliminated by disabling that module, the issue of $ being undefined is not.
