SOLUTION – JetPack Sharing incompatibility

I’ve experienced the same problem explained in an old support topic JetPack Sharing oncompatibility.

The issue is:

1. content_block types are private (to avoid showing up on search results and and prevent SEO issues).

2. Since content_block is private JetPack filters out these posts when showing the sharing meta box and when saving its value.

3. Custom Post Widget plugin doesn’t set global $post to content_block post before calling ‘the_content’ filter hook, which is used by function sharing_display() in …/plugins/jetpack/modules/sharedaddy/sharing-service.php.

One solution is:

1. Not sure if this is the preferred WordPress way of doing this, but modify the …/plugins/custom-post-widget/post-widget.php code line +102 to set global $post accurately. I don’t like modifying plugins, so please share if there is another way to do this inside the theme’s functions.php file. Or, if adequate, I suggest Johan includes it in the Custom Post Widget plugin code.

if ( !$apply_content_filters ) { // Don't apply the content filter if checkbox selected
        global $post;
        $post = get_post( $custom_post_id, OBJECT );
        setup_postdata( $post );
	$content = apply_filters( 'the_content', $content);
        wp_reset_postdata();
    }

2. Add these two functions to your theme’s functions.php file

add_action( 'add_meta_boxes', 'mytheme_add_meta_boxes'  );
    add_action( 'save_post', 'mytheme_save_post') );

    // Add Meta Box to Custom Post Widget Content
    // JETPACK: +66 sharedaddy.php - function sharing_add_meta_box()
    function mytheme_add_meta_boxes() {
        global $post;
        if ( empty( $post ) ) {
            return;
        }

        $post_types = get_post_types( array( 'public' => false ) );

        // Post Type Exception
        $post_type = 'content_block';

        if ( in_array( $post_type, $post_types ) ) {
            $title = apply_filters( 'sharing_meta_box_title', __( 'Sharing', 'jetpack' ) );
            if ( $post->ID !== get_option( 'page_for_posts' ) ) {
                add_meta_box( 'sharing_meta', $title, 'sharing_meta_box_content', $post_type, 'advanced', 'high' );
            }
        }

    }

    // Save Sharing Meta Box Value
    // JETPACK: +139 sharedaddy.php - function sharing_meta_box_save()
    function mytheme_save_post( $post_id ) {
	    if ( defined('DOING_AUTOSAVE') && DOING_AUTOSAVE )
	        return $post_id;

        // Record sharing disable
        $post_type_object = get_post_type_object( $_POST['post_type'] );

        // Post Type Exception
        $post_type = 'content_block';

        if ( isset( $_POST['post_type'] ) && ( $post_type_object = get_post_type_object( $_POST['post_type'] ) ) && ( $post_type_object->name == $post_type ) ) {
            if ( current_user_can( 'edit_post', $post_id ) ) {
                if ( isset( $_POST['sharing_status_hidden'] ) ) {
                    if ( !isset( $_POST['enable_post_sharing'] ) ) {
                        update_post_meta( $post_id, 'sharing_disabled', 1 );
                    } else {
                        delete_post_meta( $post_id, 'sharing_disabled' );
                    }
                }
            }
        }

        return $post_id;

    }

https://wordpress.org/plugins/custom-post-widget/