I think it's probably the story structure that caused this problem for me.
On the one hand, switching between viewpoints allowed the mystery to unfold in a really cool way. It was a clever way to progressively reveal more & more while keeping the explanation for the end.
It really undermined the emotional heft of the story though. I didn't feel I got the chance to invest in the characters. I guess I felt the most for Alex, but you get so far into the film before getting to know him.