UA 988 departed FRA Sunday with two seats left open upfront and with myself second on the upgrade list. I'd already had my upgrade clear partially from Y to Premium Plus and had assumed the rest of the upgrade would not go farther when J showed up as checked in booked full, but it looks like two people no-showed. I spent a few minutes wondering if somebody would show up in my row with a freshly-printed boarding pass, but after noting that a) the crew looked very busy trying to get the flight out on time, b) I was pretty full from visits to two LH lounges earlier in the day and c) I was curious to experience Premium Plus internationally, having never done so before, I decided to let the situation play out. And it played out with those seats remaining open, as I could see in the seat map (which didn't show any blocked) and by peeking into the Polaris cabin.

Anybody want to guess what went awry in that situation? Could the seats have been broken? (I didn't get to see if there were any labels on them as I deplaned, because I was on the wrong side of this 773.) Or was this just a case of a busy crew skipping that last check, and I--or the person at the top of the upgrade list--should have waved over an FA or hit the call button once check-in time for the flight had closed?