The “submitdiv” metabox is being removed for all the “wp_statuses_get_supported_post_types” custom post types, including the “custom-css-js” post type used by the Simple Custom CSS & JS plugin.
We’ll add a filter call on our side to remove the “custom-css-js” post types from the “wp_statuses_get_supported_post_types” filter within the next plugin release (3.42). That will solve the conflict with the missing “Publish” button.