Flying SEA to EWR, with 36min to departure time first shows full with 15 out of 16 passengers checked-in.

I'm essentially waiting for the last F pax to no show so I can clear the UG. ​​​I'm #1 on the UG list and I board the plane.

One min after at 35min to departure #2 pax on UG list clears. I'm still #1, but now F is full.

​​​The only reason I notice is because I took screenshots of the UG list the day before, about 36 min before departure and right after #2 pax cleared.

Could #2 have bought up the upgrade? Most likely not as F was full and there was still 5min prior to check in ending 30min prior to departure.

There was no seat to be bought until either the gate agente dropped the last F pax due to now show or the system did. Either way #2 pax would have had to immediately paid for the upgrade within<1min of one seat freeing up. (Why? Because I was refreshing that list every 30sec in the last 5min hoping the last F pax would no show.

My hypothesis is that the gate agente skipped me and jumped #2 to F ahead of me. Pax could not have been an F sitting in Y as there were 6 seats open at one point the day before. Useless PP with 1k on B fare not enough to clear the UG list.

Any thoughts? Other possible hypothesis?

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