Undefined index

PHP Notice: Undefined index: s in /home/ricmessi/public_html/wp-content/themes/architecture/inc/library.php on line 448

why do I get this message in the server log?
already I changed my host 3 times and always shows this message.

Hi!

Could you give us the page URL where you get this message? I've checked the theme and couldn't find this notice even after enabling the WP_DEBUG option.