you mostly likely hv a schedule change on a partner airline
If your itinerary involves partner airlines and they have schedule changes, you could have been automatically rebooked, but tickets NOT reissued, and you will have that message and the disappearance of your itinarary.
A phone call to AAdvantage desk would easily take care of such.
We had that happened earlier this year when IB cancelled our flight, but rebooked us on an earlier flight, our reservation disappeared and I got the message. When I called AAdvantage, the agent immediately saw the tickets were not re-issued, and took care of that right away. Itinerary reappeared.