I like Takodachi's link for it's organization, but I feel it's a bit too nice to Ichiraka in this situation. Edit: In fact, I don't actually like the authors of it, Nijicord to me means the 4chan /niji/ threads or the Niji reddit, who are clearly biased in favor of Ichiraka.
Roa got mad over Meiro, a new talent in Nijisanji having the same regional dialect and verbal tic, as Roa had turned those into a sort of "demon language" for her character. Meiro auditioned verbal neutral because she wanted to make a good impression, but that fell to the wayside when she debuted due to nerves, this is understandable. Roa gets mad and knowing she's a bread winner in Ichiraka decides she will make this an issue and weaponizes complaints to the company and her manager and eventually culminating in taking to Meiro that she is to stop talking like Roa. Meiro is just as crazy as Roa and so she gets stressed out and blows up. Well a woman scorned has more wrath than Hell and she goes to Narukami with her side of the story and some discord chat log screenshots.
JP Nijifans are very dedicated to the company image as opposed to Hololive fans. They at first went after Meiro for making the company look bad and then when this blew up, chased Roa for also making the company look bad. There had been long time rumors that bullying for sure happened in Nijisanji, Aloe Mano even talked about a former Niji who got bullied in her now infamous Twitcast pre-debut stream that the idol and Vtuber communities in Japan scared her. This story broke out shortly after Aloe quit and that only made it worse.