Getting the Support ID in the response header

The issue I am facing is that on AJAX pages, the HTML is not executed. We can get to the blocking response page by either specifying a response type of "Redirect URL" or specifying a custom response header (see below):

HTTP/1.1 301 Moved Permanently
Location: https://qa-resweb.passkey.com/UnexpectedError/SecurityBlock.jsp?F5ID=<%TS.request.ID()%>
Content-Type: text/html

The problem is that in either of these cases, the support ID does not appear. Any further ideas?

(BTW, the custom response HTML is exactly like that in 7825, that is:

)