[Plugin: Category Shortcode] expects get_thumbnail

Probably not just me but this plugin when parsing the posts in the Category expects that the theme has support for “get_the_post_thumbnail()” you aren’t checking for this and if not then it breaks the code and nothing gets returned. Several lines in your loop to process the posts in the category are like this:

$rdscf_output.='<div class=csc_post_thumbnail>' . get_the_post_thumbnail($rdcsc_posts->ID, 'thumbnail') . '</div>';

For others who may not have this newer functionality you get get it by putting this code within your theme’s function.php:
<?php add_theme_support( 'post-thumbnails' ); ?>

https://www.ads-software.com/extend/plugins/category-shortcode-w-generator/