The theme option setting is not for shortcode.
For shortcode, it will respond to the values set in it’s attributes.
In your case, it does not work because there is a conflict with your site origins panel plugin.
As a workaround, you can write a custom excerpt by using the “Extracto” input.
I had written the sentence “This is a custom excerpt” in the following post’s “Extracto”
It’s showing up in your post on your blog grid.