See what function is causing a redirect in WordPress

mu-plugin-clarify-redirect.php

<?php
add_filter('wp_redirect', 'clarify_redirect');
function clarify_redirect( $url ) {
  $callers = debug_backtrace();
  foreach ($callers as $i => $caller) {
    header("X-Caller-{$i}: ". $caller['function']);
  }
  return $url;
}

This will hook into the wp_redirect function and provide information in the headers of the page that is redirecting, not the page that WordPress is redirecting to. Though the visitor will not see these extra headers unless looking for them, it is wise to only use this for debugging purposes.

You can view the headers yourself by either using a developer tool in your browser with the option "persist" on, or you can use cURL on the command line of your OS (Mac OS X or Linux support cURL out of the box, for Windows you might need to install it first - not covered here)

curl -D - "http://yourdomain.com/your-redirecting-page"