I am flying Air NZ business on the 777.

Selected 7K as I've had it in the past and I like it. The day before departure I had a look at the app and saw that my sear had mysteriously changed to 9K. Tried to change it back to 7K as it was showing as available but every time I did so the system just popped me back into 9K.

Fast forward to today and when I went to check in I asked the check in agent if 7K was available. Yes was the answer and I was given a boarding pass for 7K. At boarding they are paging my name and when I get to the counter they tell me "sorry we have to move you to a different seat". "Ah, I see" mesays, "the seat must be broken". "No", I am told. "Someone else is sitting there". Sure enough when boarding, I see that there is someone in 7K.

Out of curiosity, learned folks, what do you think caused this? I am a bit miffed to be fair. Is it because I am lowly Gold and an Elite member asked for my seat?