I think there is a bug during the trial of raven at Wenlocan outpost. Some guards are surprisingly not attracted by whisting. When I'm hidden crouched in the grass behind the wooden pillars (but with some space to enter into the grass), I whistle to attrack a nearby guard, however instead of coming to me to check what's going on, he goes somewhere else to climb up the ladder to the platform and doesn't seem to come back. The problem is, that he seems to disappear! At my first succesfull attempt, I haven't calculated assassinations but at the score screen I realised I miss one assassination (I was pretty sure I eliminated everyone I could see). So I repeated the trial, however now, before collecting the last artifact, I checked if I miss it again by calculating the score and it turned out I again miss one assassination. So, before picking the artifact, I came back to the camp, looked everywhere and there was no guards, i.e. every single one has been assassinated. Yet again I missed one assassination for gold medal.
I thought of this a bit and I realised that the abovementioned guard might be missing since I don't recall eliminating him. So I decided to change the approach. Instead of attracting him as my second target, I attracted his as a third one. He still did the same but now I could assassinate without being detected. The problem was that now, another guard didn't act as I think he should (come to the grass to check when I whistle). Instead, he also went to the ladder (the same situation as with my second prey), however I could eliminate him on his way to the ladder. That was extremely risky, since there was another guard who could detect me. Luckily, the game worked in my favour this time (to be honest, I think this also was bugged since I think I should have been spotted at this time. I really have no idea why the bar turned red, battle music started to play but I remained undetected...). This definitely shouldn't work like this.