Thumbnail not appearing

Using the shortcode at the bottom of a Page. The shortcode is:

[catlist name=workshops thumbnail=yes thumbnail_class=lcp_thumbnail]

The page is https://scottthomasimages.com/photography-workshops, and the thumbnail is not appearing.

Looking at the code, it appears that the thumbnail class “lcp_thumbnail” is not showing up in the code.

Is there something I have missed?

Thanks for your help.

https://www.ads-software.com/plugins/list-category-posts/