If I edit my careers header part there is a field for Custom Profile Url
and the preview below is:
Prod.careers.stackoverflow.com/l33tname
Which should be careers.stackoverflow.com/l33tname
Screenshot
Thanks for letting us know. We switched over from our New York data centre to our Denver one recently, and this was a small difference in configuration between the two environments. I've corrected the setting now.
Prod.careers.stackoverflow.com
works fine internal but it's not a external url