Same here. Since SU2, most of the flights not registered in the logbook.
If I complete 2 flights, the first one vanishes from the log right after completing the second flight. After restarting the sim, the first flight also vanished from the log.
Also, some of the flights I completed weren’t even registered right from the beginning.
All the flights were free flights.
According to other simmers, this bug appeared already in the beta stage of SU2 and keeps on in SU3 BETA, proving that zero fcks given when people mention such basic bugs.
Also, flight hours always reduced with every new flight deleted from the log.