I'm not sure if this has been discussed but... I had 15A on UA882 BKK-ORD on 1/23. Same 744 all the way. But they have now switched to a different 744 in NRT and my 15A disappeared. I just called and got 15A/BKK-NRT and 15H/NRT-ORD. But if you're on a similar flight it's worth checking. I noticed when I was reviewing My Itineraries and saw UA882 with Flight: Confirmed but no Upgrade: Confirmed for the UA882 portion and the Seat was listed as N/A.

This is still UA882 straight through, but the equipment switch will lose you your confirmed UG on both legs.

My flight out ORD-BKK on UA 881 was not affected.