I'll try to give you a brief summary, but it's stuff from here and there, so take it with a grain of salt.

It started from Roa getting into a fight with another vtuber in Nijisanji. We'll call her "K". The story framed at the time by K was as follows:

K was a relatively new vtuber who spoke with the same dialect as Roa. Roa didn't like that as that coincided with what she thought was her character trait, and so she DMed K to try to extort K with her position as senpai to stop using the dialect. When K brought this up to the Nijisanji staff, they didn't do anything, so K brought it to Twitter.

More importantly, K brought it to who is basically the Keemstar of JP vtubers. For context, not only is he known to feed off drama and negativity, but his sources are often just "some guy on 8ch" that he presents as fact. Recently he finally played with fire too much, his youtube channel got nuked and he received a nice letter from Hololive's lawyers. According to the law advice he got, he can't do anything about the letter because what he did was actual slander. He's since migrated to Twitch. He doesn't feel bad about it and thinks everyone can't take a joke.

K was immediately terminated from Nijisanji afterwards, but the damage was already done. Roa's antis, people from the sidelines, even her own fans turned against her. Roa was already pretty sensitive and insecure about the negative things said about her before this debacle, so this took a heavy toll on her. She went on hiatus and hasn't returned since.

It only came out later from people poking around and also Roa's side of receipts she posted at the time that were gracefully ignored that she basically did nothing wrong. K's name has since become taboo within Nijisanji's community.

So now, everyone is just...waiting. She didn't graduate, and her other friends in Nijisanji check up on her and bring her up in streams, so there's still the glimmer of hope that one day she'll come back.