Drupal Darko helps you out: Kint function is running slow or timing out
If you use the kint() function to debug Drupal 8, you may experience that it is slow, or times out. To fix this problem you need to reduce the level of nesting.
So in your settings.php add the following:
require_once DRUPAL_ROOT . '/modules/contrib/devel/kint/kint/Kint.class.php'; Kint::$maxLevels = 3;