That is exactly what I believe happened. I booked, and the system bucked!
Unlike you when I picked up the disconnection, and phoned AA for help, there was no inventory left.
They are BA flights using AA’s FF miles, so I was able to see that the 2 award seats available at my time of booking then had disappeared off the BA site, when I checked next morning. I assume in some way related to my booking.
BA say it can take a day or 2 to go back on their inventory, so I have not given up yet, that I might get a second bite.