plugin template replacement for single.php does not show with Sage as the theme

using Sage 8.5.1 https://roots.io/sage/ as my starter theme, the custom post type template defined in my plugin is not shown (I get ‘base.php’ as the template when it should show ‘single-featured_entree.php’. [full Template relative path: plugins/featured-entrees/single-featured_entree.php] )

The correct template file (as defined by my plugin, which allows for the theme to override it with an equivalently named file) IS still used to display the extra fields from the custom post type, however.