following your main page HTML elements :
#ez-toc-container .ez-toc-title-container .ez-toc-title-toggle #uniform-item #item
You will see that checkbox(#item) element have a CSS left value equal to -999em
So all you need is to reset that value (that won’t effect the design, but it will help fixing your out-screen layout issue)
You can do it adding this CSS code via the wordpress customizer page
Page Link:
https://YOURDOMAIN/wp-admin/customize.php
replace “YOURDOMAIN” with your domain
Then > Additional CSS and then paste the following code and then click on Save :
#ez-toc-container .ez-toc-title-container .ez-toc-title-toggle #uniform-item #item {
left: 0 !important;
}