The airport staff had no clue how it happened. Strange that a correction message was not even sent. The load was already expected to be light, so I could not find out if pax missed the flight and had to be accommodated on the 21:15 flight. Two J pax who almost missed the flight were accomodated in F as compensation (plenty of empty J seats) but with J meal. That disturbed service. FA had to separately prepare their J meal. They took their orders, brought trays from the J galley. The guys (I knew one) were quite excited by their upgrade, engaged in a wine tasting party (F wine) and were constantly chatting with the FA who spent a lot of time. It resulted in slow and disorganized F service. Unpleasant for a paid F pax like me.