Custom Sidebars Pro plugin causes "unresponsive script warning" when I go to Theme>Cust

Hello there!

Going to Appearance>Customize yields me ye olde spinning beach ball and the following:

Warning: Unresponsive script. A script on this page may be busy, or it may have stopped responding. You can stop the script now, open the script in the debugger, or let the script continue.

Script: http://homeschoolbird.com/wp-admin/load-scripts.php?c=0&load%5B%5D=jquery-core,jquery-migrate,json2,plupload&ver=4.0:2

Choosing "Stop" or "Continue" does nothing, and I'm unable to close the window or go back. I don't know how to use the debugger.

I deactivated all plugins and then reactivated them one by one, and Custom Sidebars Pro is definitely the problem child.

I've granted support access. Can you help?

Thanks in advance! :slight_smile: