I had something similar happen on my last flight although I was not affected since I had paid for F (last flight of the day DEN-IAH). From what I saw one upgrade was processed before boarding, and it said 1 blocked before the boarding process started. Late connecting flight caused us to wait about 15 min. 1A and B open, late passenger in F boarded and took 1A, but 1B went out empty although the upgrade list was at around 25-30. Perhaps not enough time for GA to process the last upgrade since they expected 1B to make the flight, but didn't? Also, can't explain it, but I have a feeling this was the GAs first.