I FIXED IT
So, you know how there are nine files numbered 1-9 inside the speech folder? I suspected the bugged subs were playing the voicelines double because they "chose" two of these folders at the same time. And so, with a lot of trial and error, I rooted out which sub is using which folder and found the solution. "Simply" remove all of the speech-folders except 1,2,3 and 7.