Hi @Aleksej-Original,
Thank you for reaching out to us. This is basically not an error. It is a notice alerting you that UberMenu was loaded on the window load event rather than the document ready event. This usually happens when there is a JavaScript error on your site. Try removing custom JS (Theme Options > JS or in Cornerstone’s JS section) or third party scripts you’ve added.
If this doesn’t fix then there must be a third party plugin conflict. You should then try testing for a plugin conflict. You can do this by deactivating all third party plugins, and seeing if the problem remains. If it’s fixed, you’ll know a plugin caused the problem, and you can narrow down which one by reactivating them one at a time.
To learn more about this notice, please see https://sevenspark.com/docs/ubermenu-3/faqs/initialized-via-window-load
Let us know how it goes!