This has been happening to me a good amount lately and I don't know why. I've been calling before the 7 day window and requesting an isle, only to notice that, at online check in, my seat has been unassigned. Much of the time I'm forced to sit at a window because as many of you know, the preference seems to be the isle seat.

The only thing that I can think of is that my corporate travel agency had window in my profile and that could've done something during the automated upgrade process.