Kleo theme has a feature that checks messages and notifications only when BuddyPress plugin is activated.
If your website has significant traffic it may be needed to increase the AJAX interval refresh from Wp-admin -> Theme options -> Buddypress -> Live notifications interval and add a higher value like 60000 (60 seconds).
Also there it’s a programmatically way to do that by adding the next snippet to : wp-content/themes/kleo-child/functions.php
NOTE: Child theme needs to be installed and activated.
COPY CODE
/* Stop refresh interval to JavaScript app.js */
add_filter( 'kleo_localize_app', function($data){
$data['bpAjaxRefresh'] = 0;
return $data;
} );