I mean, Kase says that's the issue in Mint and Kase-san. She explicitly says that she's worried about Yamada's body and that she's been working too much. Yeah, missing the race was bad, but that's not the main issue. It's that Yamada is focusing more on working for Kase rather than Kase herself. She wants to get all these nice things for Kase and is ignoring what Kase actually wants, with that being to spend time with Yamada.
Action speaks louder than words. Kase mentions that she was worried about Yamada and wanted Yamada to rest, but then right after she did, she made sure to tell Yamada:
"I might've gotten a better time if you were there, Yamada."
Now why would Kase tell Yamada that, if missing the race wasn't the main issue? Even after that, Kase goes on rambling about how Yamada's job is more important than Kase's race, sure she mentions she wants Yamada taking care of herself, but keep in mind the only reason Kase blew up at Yamada was because Yamada had said that it didn't matter that she was there or not. Not to mention, in that entire exchange Kase didn't once ask Yamada, "how she was doing? Or if she was alright?" She immediately went into questioning mode on why Yamada was working.
Then in this chapter, we see that Kase only responded with Emojis to Yamada's messages. As far as we know, Kase hadn't asked if Yamada was doing well, or to get updates on whether Yamada was taking care of herself. Heck she could've even asked their friend/neighbor to keep an eye on Yamada, but as we can see in this chapter, the friend is pretty clueless on the situation unless Yamada tells her.
So in short: Kase 'claims' that the issue was Yamada going to work instead of resting, but her reaction as well as actions suggest otherwise and that instead Kase is mad that Yamada 'chose' work over her race and is now throwing a tantrum, and making no effort to check on Yamada's condition. If she was actually mad at Yamada working, and properly showcased her concern, then I'd have no issue with Kase. But the fact that she underlined the whole "missing her race" so childishly...
I think maybe it's because I wasn't actively reading until after the whole arc with Kase was done and they had moved in together, but I just don't get this hate for Kase. Yeah, all the stuff she did with postponing the apartment was really annoying, but I don't think it means she can't be in the right in this instance. Yamada is working too hard and her priorities are all out of wack. Like, the arc that caused people to be upset at Kase in the first place was centered around the fact that the two wanted to live together. But now, Yamada spends so much time working that she isn't even really living with Kase at all.
There's a lot of issues, but I'll keep it simple. The biggest issue I have with Kase at the moment is that she had no period of self-reflection like Yamada just did in this chapter. You said it yourself, we're seeing a similar situation in which the two of them want to spend time with each other, yet their actions in both arcs pretty much made it difficult to achieve that. The biggest difference is how did each of them react to both situation:
In the case of Kase racing against her roommate; the consequence of that action have caused Yamada to miss out on the home that she wanted to get. Then when Yamada confronts Kase about it and asked if racing the roommate was more important; Kase didn't treat it seriously and instead just acted as though Yamada was being adorably jealous. Kase didn't once show any self-reflection over her action. We didn't have a chapter of her realizing the reason why Yamada was upset, or the difficulties that she was going through, or even a flashback at how Yamada was excited for the two of them to live together, then for Kase to realize that she herself was the one who caused the issue.
Meanwhile here; the biggest issue is Yamada overworking herself, however that's not how the story is treating it. It's treating it as though the biggest issue is Yamada not spending enough time with Kase. You see this with how Kase reacted when Yamada said it was alright if she missed the race since Kase did so well, and when Yamada had her self-reflection, or when she was speaking with her neighbor/friend. It all boiled down to her not spending time with Kase.
Long story short, it's essentially how one-sided the story is being.