Just happened to me. Expertflyer showing C1 tomorrow (9/9) flight 98. Agent says there is no availability. I'm on one of AA's dumb 'direct' flights - 98 TUS-ORD, 5 hour layover, then ORD-LHR. These have caused upgrade problems in the past.

When I force Expertflyer to show the direct flight it is J0. Looking at individual segments A4, J7, C1.