Common lobby for 2 gates

My flight to Jakarta used gate C25. It uses a common lobby with C19 but there are 2 separate doors and 2 separate screening gates. The door to C25 is closed and the screening gate is unattended. Many passengers to Jakarta were waiting outside, confused. There is a queue waiting to be screened at C19. I asked a security staff why C25 is still closed. She said that it uses a common screening gate as C19. To her, this is "understood". She did not realized that many passengers were confused and waiting outside. This "brainless" behavior is quite common.