I've almost played through the game and there is one QTE event which I do not really understand. It is the one where you hit left and right button as fast as possible. Is there anyone else then me that experience that sometimes you fail when you are totally on top of the bar, and other times you succeed when managing to move it up alot less?

These are the ones you do with Carla? If so, you have to press slowly left and right to keep the bar at the center, it took me some time to understand this.

Yeah, it's gotta be evenly pressed in rhythm with the indicator arrows. Otherwise, you'll fail every time. I learned this the hard way. Effing Naser and Jones scene.

A lot of the QTEs just seem extraneously added to add more "function" to it and make it seem less like an interactive movie, imo. I wouldn't complain, but the Simon Says QTEs don't really give you a lot of window to get things right, imo.