On a recent flight I was traveling solo and was #1 out of 5 people on the upgrade list shown in the app the evening before departure. Flight was selling F5. In the early morning hours on day of departure, the top three of us disappeared from the list. I got the "you've been upgraded" email and selected my F seat (presumably they did too). Got to the airport and pulled up my BP and whoa, I'm back in a coach seat. Even more odd is that the upgrade list in the app now showed the people who had been #2 and #3 on the list the night before still in F seats (i.e. they reappeared on the list after having fallen off), and now I was #3 on the list in Premium Class seats along with #s 4 and 5.

I get to the gate agent and she apologized; they swapped a 738 in for the scheduled 739, we lost 4 seats. I asked why they picked me since I had been first on the list the night before. She shrugged and said "the computer tells us who to pick, they must have higher status than you. But don't worry, we gave you 3,000 miles for the inconvenience" It was an outstation and there didn't seem to be anyone else to ask for better info or to intervene. The next day I called Customer Care and they didn't have any more insight either. (I get it, they -- and we all -- have bigger issues right now in 2020)

Just curious whether anyone has insights into why the app Upgrade list would change order like this...? I know there is a separate Day of Departure upgrade list that is sorted by different criteria (including time of check in as a tiebreak), but I thought that's what showed on the gate screen and not in the app??

Did the fact that I didn't check in right away at D-24 hurt me? (I usually do, but for some reason didn't this time)
I've heard in the past sometimes they just bump the people who were in Row 4... but that was not the case for me.

Thanks in advance for any insight