Just finished watching this.
I'm not sure how I feel about it. They did well enough at creating some tension but the overall story and resolution just felt lacking.
The idea behind a thriller like this, in my mind, is usually for you to discover the solution to the problem alongside the characters. Misdirects are fine but to have information completely unrelated to the solution revealed right at the end as though that is how you should solve it really hurts the vibe.
The consistent flashbacks also show that they needed to do something to try to help guide the audience to an answer. In the end it isn't a reasonable conclusion with the information presented. It's meant as more of a "haha gotcha!" outcome.