Every time when I try the OoB sewers route and get to the point where Samuel should be waiting, he's missing and I can't finish the mission. 
Does anyone know what triggers that?

I've recently started to get into this speedrun/speedruns in general. Since I'd never recorded one bevor I'd tried a setup for LiveSplit. In order to try it out I played through the intro. But as I'd get to the cutscene with the Empress and the Lord Regent, it faded black like normally, but didn't fade back. I've could see nothing, except the quest marker, but could still move. This way I could give the Empress the letter and the cutscene ended immediately. I've done a quicksave, reloaded it and could see again. I don't know what triggered this since I'm not aware that I may have done something different, but thought it may be helpful.

Sorry for the little/no information and the bad english.