Cinematic camera fades in and out for 2 sec - can't find an option to disable it

Hello, I started to capture movie from a Cinematic camera on rails, I did select Auto-Exposure to min=1, max=2 and I also have selected AutoExposure on PostProcessing same min=1 max=2. But when I was clicking on Capture-Movie, I see there is a fades to black in the middle of the video for around 2 sec. Why it’s doing it, I don’t understand. Can’t find a solution for now.