I am having this problem right now. Looking into a MR on July 3 DFW-SFO-DFW to take advantage of the DEQM promotion (I am a Texas resident but temporarily live in Colorado for work). ITA Matrix shows $319 ai. Booking these flights on AA.com is a nightmare.

Doing the initial search for DFW-SFO RT by Price & Schedule. Several flights are available at the $149 price. Click on the 9:05AM flight, click "Continue": "...flight or fare no longer available." Ok, try the 10:05AM flight. Same thing. Next down the list is the 7:40AM flight. Ok, seems to work.

Now on to the return flight. There are two flights at $148 listed. Click on the 3:35PM.... no longer available. Click on the 5:40PM.... no longer available. So that's both of the $149 flights gone, but even so, the tab at the top shows "Return: Sun Jul 03: From $148" with both fares showing as unavailable, and no $148 flights listed on the other pages.

Ok, I switch to another browser. One where I have never logged into aa.com before and with all cookies cleared. Same thing happens! The $149 fares still show up initially, then disappear upon clicking them! If they're "no longer available" then why do they show up again, only to disappear again?!