Had a situation last month on an AA flight BOS-LAX, booked in First with wife (on same PNR) and at check in given boarding pass with seating in different rows, check in claimed they could not move us as cabin was full, one boarding I was 2A and wife was 3F, I offered to swap with pax sitting next to wife and met with a refusal from the paxl, then tried for wife to swap with the pax next to me, again met with a refusal from the pax next to me.
Not sure why this happened when we were both on the same PNR?