I have heard little things here and there about a private server that managers are not in, and while I think that is definitely a thing that exists, management was totally notified that this stream was happening. Livers have gone on record saying that schedules have come out late or that the schedules have been switched around due to management. If what Millie has said is true, then this idea has been on the table for at least two weeks and has had ample time to be shot down if they thought it was a terrible idea.
As for the whole Selen is being left out shit, it mostly stems from the fact that Selen, and Obsydia in general, don't seem like the closest group of friends, and that there are obvious little cliques in EN. You have the whole Hanamori gang that is close together, and then you have Millie's little gaggle that includes her, Enna, Fulgur, and sometimes Kyo. People noticed that Selen is not in many of these little groups and that the only person she seems close with is Pomu. This created the rrat that she doesn't hang out with anyone in EN besides Pomu, which isolates her, and that the reason she only hangs out with Pomu is that no one else wants to be friends with her. This obviously isn't the case, cause she seems pretty close with NijiCanceled, they have talked about off-collabing and playing CAH offline, and others in the branch have talked about how nice and funny Selen is. Selen also takes on projects all the time, a problem she herself has noted she has, so maybe that explains why she isn't the most talkative person in the group chat, but she isn't isolated or an outcast.