Perms was the first guess, but they usually aren't shy about saying streams are cancelled due to perms or tummy hort. Promising to explain on stream later does sound like the postponement was because of the termination announcement. If so, Cover learned at least one thing from Rushia's termination: tell the ENs and IDs in advance so they don't tweet quite as many expletives.
The significance is that she has screwed up and used Mel stream assets on her PL before, but as other Holos have shown, that's not a firing offense.
For autistic documentation,
the old English version was up until at least 09:22 UTC.
The update was no later than 11:16 UTC.
At first, I agreed with Nano's interpretation, but now I have my doubts. The claimed breach "leaking information that she acquired from the company to third parties" is more specific than Yuri's termination notice. Even if we don't know what was leaked, how it was leaked, or to whom, I'm not sure what remedy could have been proposed (obvious jokes aside), and if there was a proposed remedy, why Mel would decide it was not worth 5 years of work.
Choco and Lui are live now, cooking for Iroha. I can't understand them, and Choco may be making sure the show goes on, but she seems fine.