Setting csrf_regenerate as TRUE

First I spotted this on the jQuery website regarding ajaxSetup
Set default values for future Ajax requests. Its use is not recommended.

If I understand correctly, the use of this function will effect all following AJAX calls.
Once it has been declared the values are not updated.
So yes, I think this is the problem and you should not use it.

Create your own set and get functions for the CSRF

PHP Code:

<script type="text/javascript" language="javascript">
    var csfrData; // Declare globally
    csfrTokenName = '<?php echo $this->security->get_csrf_token_name(); ?>';
    csfrHash = '<?php echo $this->security->get_csrf_hash(); ?>';

    setCSRF(csfrTokenName, csfrHash);

    function setCSRF(name, value) {
        csfrData = {}; // Reset csrfData to an empty array
        csfrData[name] = value;
    }

    function getCSRF() {
        return csrfData;
    }
</script> 


And from the AJAX call you of course call the setCSRF function with the returned CSRF to update