Yep I have the same error every first time a page loads.
This happened after Elementor’s last update this morning.
Notice: Undefined index: _ob_harakiri_height_tablet_tablet in /home/www/wp-content/plugins/elementor/includes/base/controls-stack.php on line 1418
Line 1418 ——-
// If the control is not desktop, take the value of the conditioning control of the corresponding device.
$instance_value = $values[ $pure_condition_key . $device_suffix ];