No post classes inside singular custom post type page

Hi,
I wonder why there’s no class attribute with post_class() callback inside article tag of custom post type?

I’m using “WP Job Manager” plugin for job listing post type, and I see that Oceanwp is loading the layout of “single”, but inside “layout.php” the function post_class() is not used at all.
I want to apply custom classes to the article itself. I can only do this inside body class…