I am flying to SFO next week from CDG. Got my seat for that one no problem. However, for my trip back via ORD (SFO-ORD then ORD CDG) I could not get seat assignment on the web nor when I called UA. I was told that the seats were blocked and would be assigned only at the airport.
What is the reason for blocking seats ? Does this mean that no one has been assigned seats or simply that the percentage of seats made available in advance have all been taken ?
any infos would be appreciated.