HTTP health check: Manual GET result versus what's seen in Fiddler

Scenario: Replace the generic http health check to a menu page with something specific. The issue is the page in question redirects to a login page on a different site before returning to (and actually displaying) that menu page.

Using Fiddler I can see the html of the initial page before it redirects, however when I manually send a GET from the F5 for it I receive a '200 OK" along with <title>Page Not Found</title>. I was expecting to get back the same html I see in Fiddler. Is this due to the redirect futzing with the GET request?

Has anyone run into this situation before?

Thanks!

Note: This is the GET I'm using: GET /pls/prod/twbkwbis.P_GenMenu?name=bmenu.P_MainMnu\r\nConnection: Close\r\n\r\n