Had a brainwave while reading this chapter.
So, Shuta, Miyashita's ex, is from a different class (class 5). So is Nogawa, albeit her class is unknown.
Now, I've had this thought. What if Shuta and Nogawa are both classmates in class 5? And what if there was some sort of tension between them, perhaps related to Miyashita in some way? Nogawa's reaction to seeing Miyashita in ch1 is pretty suspicious. Sure, it could just be attributed to her being surprised that someone was watching them fight, but the way she rushed past Miyashita implies there's more to it.
As we know now, absolutely nobody knew about Suzuhara's relationship with Nogawa (despite the implications that they might've been dating since their 1st year of HS and possibly earlier), and it seems Miyashita's even shorter-lived relationship with Shuta is similar here. Given Miyashita's expression when he told her that his relationship with Nogawa was practically nonexistent, it seems something here hit home. Seeing Suzuhara act that way at the end of this chapter, it may be possible that something about what Miyashita told him about her relationship with Shuta also hit home. I think there's potential for them to bond over some form of a shared frustration over shallow relationships with their exes.
This is all just a random thought, though, and me throwing stuff at the wall and seeing what sticks. Hopefully if Nogawa shows up again, whatever drama that may ensure won't last long. I'd prefer she not show up at all, but some of the more subtle hooks I've seen seem to imply that she will be coming back.