Flying PDX-LAX-DFW-BTR this evening. Confirmed upgrade into first for both PDX-LAX (at T-27) and LAX-DFW (at T-77). I check in 24 hours in advance, get my BPs, all is normal. I wake up at 7:30am PST and notice my girlfriend still has her seat on LAX-DFW, but my seat assignment is zero'd out. I try to re-select the seats, but it isn't letting me. I call in, and the agent is confused and really isn't helpful. The chat agent says something glitched, which Twitter corroborates. Twitter also tells me to go see an agent in PDX as they will be able to help. I go to PDX early, and the agent is as confused as I am. The seat is still available, so nothing mechanical, but she said to see an agent in LAX. I also don't have a seat on the plane as of now, but I am #1 on the upgrade list (so I lost this first class seat, I guess). The PDX agent also said that the same thing happened to another passenger earlier in the day.

I'm about 35 minutes from landing into LAX, but very confused as to what has happened. Does anyone on here know what could be the issue or have any advice?

Thanks in advance!

Update: Went to the Admirals in T5 and the agent had no idea what was going on. She called into Phoenix, and the agent there had no clue, either, although she mentioned it may have something to do with an oversell of the cabin? This makes no sense, as I�d assume those upgraded after me would have gotten the bump, instead. Will head down to the gate and see what is going on, but strange strange situation.

Don�t know if it�s the same cause, but I remember something similar happening to me last year.

Several hours before the flight, AA swapped a 20F A321 to a 16F A321 (or possibly to A320, I forget), and then a few minutes later right back to a 20 F A321, but that was enough to mess up everyones seat assignment.

Couldn�t re-select an open seat on the app. Had to get it fixed in the lounge during my connection.

Long story short, I had to go to the gate when it opened and the very kind GA was able to give me 1F after calling in to HQ. No one knew what happened, so very strange situation.

From my experience with the 321 retrofit, they blocked off 4 seats and didn't sell or upgrade (and only upgraded at the gate once the aircraft was confirmed).

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The only experience I've had with my seat disappearing was when the cabin was full with a broken seat (and couldn't be occupied) and I hadn't checked in, they assigned my seat to someone else and cleared my seat assignment (and therefore was downgraded). Perhaps you were the last to get upgraded (the rest were last-minute full F fares) and a seat was broken and then subsequently fixed. The system likely removed your seat assignment, but as you were protected (confirmed) on the flight, it wouldn't let you (or an agent) assign a seat until at the gate when the protection was cleared, preventing any other automations or agents from accidentally completely removing you from the flight.

Makes sense. In my case it was likely then the momentary swap from A321 to A320 and back.