I had a very similar thing happen to me and my companion on a flight from PDX-NRT while heading to MNL a couple weeks ago. I originally booked the flight back in July of last year and cleared into C+ shortly after booking. I picked the bulkhead seats 13F,G after the upgrade cleared and those remained my seats all the way up until about an hour after I received the "It's time to Check In" e

When I went to check in, I noticed that we had been split up and were now in C+ middle seats. I called the DM line only to be told that they weren't sure what happened and that there were no more seats available so there was nothing they coul

When​​​When I went online, I noticed they were still selling seats in C+ stating there were three left and when I checked the seat map, it showed that the middle three bulkhead seats were open. When I called back, the second agent said those seats were blocked and would be released at the gate. She said that she wasn't sure how my seats got changed but at least apologized, which the first agent did not.

When I got to the airport in SLC for my flight to PDX, I asked the check in agent if she knew why they got switched and could at least put us in the middle bulkhead. She was a lot more helpful and said there had been an equipment change and since it is all automated, they supposedly don't have control of where people get reassigned when that happens. She even showed me a little code on my paper boarding pass that identified how many times the equipment has changed for that flight (3 in this case). She unfortunately wasn't able to place us in the blocked seats but as expected, as soon as they opened the flight in PDX, I was able to have the GA move us to those seats.

It's a little irritating that the automated system apparently doesn't take status, ticket purchase time or seat selection time into account when reassigning seats during an Equipment change.