PHP parameter utm_campaign exists in URL but not in $_GET array

I am facing this (I don't know what to call this) situation I have a URL like

site.com/?utm_campaign=value&other=1&more=2

the problem is that when i

var_dump($_GET);
// prints
array( 'other' => '1', 'more' => '2');

for some reason the parameter utm_campaign is missing from $_GET array.

any ideas? the server request_uri is

'REQUEST_URI' => string '/site-com/?other=1&more=2'

its even missing in $_SERVER['REQUEST_URI'] and the server is hosted in Godaddy and the WPEngine is not being used.

there is a javascript solutions in case some one else wanted to use but in my case I require it in php $_GET.

var url_string = window.location.href;
var url = new URL(url_string);
var utm_campaign = url.searchParams.get("utm_campaign");
console.log(utm_campaign);