Yes it's annoying that AA's online/in app options crap out frequently. Calling or Tweeting are many times your only options to get reaccommodated in situations like this.

Once he was rebooked to a connecting itinerary, he was then caught by AA's rule that you can only standby/SDC on the same routing. So a one-stop through SDF can't become a non-stop or even a one-stop through CLT instead. Again a failure of AA's rules.