@okso - If you see that error on your live production site that means you have WP_DEBUG enabled in your wp-config.php file which is generally a bad idea.
That is not an error per say but a notice that you have made a customization using a filter that has been replaced. It won't effect how your stuff works now, but just gives you a notice that you may need to update your customizations.
As for the first mentioned issue, that means that a JS error is occuring on that page, can you check your browsers console tab (F12 -> Console) then refresh and try again, if you see any errors click the black arrow to show extra details then screenshot it or copy paste it so we can find the root cause, this hasn't been reported yet so it is likely an issue stemming from conflict with a specific plugin.