Something really weird happened to me a couple of weeks ago on a DUS-LCY flight. I checked in as normal using VeriFly, sent my bag through, proceeded through security and to the gate. My BP was scanned, green light flashed, "Have a good flight!" and I got onto the bus when the agent called my name and asked me to go back, saying "You're not on the passengers' list." She scanned my BP, red light appeared, and the computer said, "Passenger has already boarded." It also showed my bag as loaded onto the plane. After a couple of minutes she let me go back onto the bus. (And the bag was delivered successfully at LCY.)

Any idea what has happened here? And could this cause any problem down the line?