I called CX today to request a switch on my outbound LAX-HKG flight to the following day but I was told that I had to be placed on the waitlist. I checked EF and there are 8 seats available in I for the flight I want to be switched to. I've never had a problem changing the date before and I find this kind of strange. Any idea why I was told that the flight was full and that I had to be waitlisted?