I used the US20 miles upgrade to get two seats (2A 2C) confirmed in F a while back. I got the paper receipts mailed to me with the F seats confirmed.

About a week before the flight, I go to virtuallythere to double check and noticed that instead of 2C I got moved to 3D.

I called and confirmed that my new seat was indeed 3D. There were still other seats available in 1 and 3.

They couldn't explain how that happened.

Anyone here have a guess?

I thought it could have been because an air marshall but if the guy in 2C were an air marshall, he did a really good job blending in. Even if he were, wouldn't it make sense to take an open seat instead of bouncing someone?