The error showed on the guest captive portal. I could see the initial Login page showing up first and quickly going to the page that showed the "[ 400 ] Bad Request" error. It seems that the initial Login page was bypassed but went into error.
When I used the following script on ISE 2.2 to bypass the initial Login page it worked:
<script>
$(document).on('pageshow', function() {
if
(!(/selfregistrationcancel|selfregistrationsuccess|SELF_REGISTRATION/i).test(document.location.href)) {
$('#...
