Originally Posted by
WineCountryUA
One problem that could happened there was a faulty scan of your board pass, that would have an unfortunately action of canceling your return, so if the return is still active, them UA knows you took the flight.
Recently I’ve had flights where neither the biometric and BP scanners were working so the GA had to manually record us boarding which makes me paranoid about that situation. Now after I board I check the app to see if it indicates On Board.