Notice: Undefined property: stdClass::$version_checked

Core Control does:

add_action('pre_site_transient_update_core', array(&$this, 'handle_option_disable'));

	function handle_option_disable($val) {
		return (object)array('last_checked' => time()+3600, 'response' => null);
	}

Expected in function wp_version_check():

$current = get_site_transient( 'update_core' );
	$translations = wp_get_installed_translations( 'core' );

	// Invalidate the transient when $wp_version changes
	if ( is_object( $current ) && $wp_version != $current->version_checked )

https://wordpress.org/plugins/core-control/