This is an aa.com/IT/fare/cache issue that has been around forever and pops up every now and then, especially with more complex searches involving partners.
You can try piecing the flights together with Google Flights to see if it can combine them for whatever the "real" price is. Otherwise call AA as mentioned, although the "real" price that an agent can book may or may not be whatever aa.com is displaying that errors out.
https://www.flyertalk.com/forum/amer...aa-site-3.html