Customize under Appearance no longer loads correctly

I have installed your Smart Posts Lists Light plugin and use it along with the Widgetize pages plugin. Whenever I go to “Customize” under Appearance in the WordPress admin panel, the left sidebar mostly loads, but stops before it finishes loading the new “widget” options at the bottom of it. The page preview itself never loads in the window. The only way I can get this function to work again is if I disable the Smart Posts Lists plugin. I have this plugin in use on my home page, but it doesn’t work no matter what page on my site I load the “Customize” admin page from.

https://www.ads-software.com/plugins/smart-post-lists-light/