Airi confirmed that she's taking this break because she hasn't been doing well, and she doesn't want to bring a "doomer" mood to her streams. She did say during the break, she will probably take time to plan out future streams. She's also planning a nostalgia stream with Shiina, so that should be fun.
As for the cause of the break, she didn't go into details, and even said she probably can't go into details. She said she's been having issues in her personal life, and she said work as been a huge issue. Another thing to note is that she said she should return next week, but there's no guarantee. She said hopefully the break doesn't get extended. Not sure what that means. Hopefully nothing too serious.
Whatever it is, by the end of her chatting, you can tell she was struggling to hold it together a bit. I'm sure she'll be fine by the end of whatever is going on/her break, but I hope things get better for her a lot sooner than later.