
Yeah, that was pretty cruddy writing on the author's part. Building up that plot point and then dropping it like that makes it feel like it had no meaning in the first place and made us readers feel very confused and unsatisfied. It's especially bad because it was basically the main plot point that was driving the story forward (in such that it was what lead to the start of the story and I was assuming the story/season would end when it was resolved).
Unless your story has themes of nihilism or something similar you can't just build up to a major plot point like that and then drop it and expect the readers to just accept it with open arms.
Who didn't like the idea of Siyeon's ex (Ma WooJin) who caused him to be in debt and become an assassin just die off-screen? They revealed that in chapter 37. I was hoping for a plot twist that he didn't die and is the last villain. But nope, there was no mention of him after that. So he's still dead till the end.