what does this error means?

Hello, I can’t edit my forms suddenly , I made a compatibility test, deactivated all of my plugins and no result. so I downloaded a debugging plugin called ‘Debug bar’, after running the test, resulted many queries and two J.S. errors, one of them is as follows:

Uncaught TypeError: jQuery(…).sortable is not a function
https://my website/wp-content/plugins/ultimate-member/admin/assets/js/um-admin-dragdrop.js?ver=4.8.1 line 1

what does that mean? how to fix it ? is it the reason of my basic problem (editing forms)?

Note: This is the third or forth time that I publish a support issue with no response, is this the right place here? or I have to go some where else (facebook or twitter for example)?