Like the title says, after opening your condo from either a server or the menu, the server chat disappears. I'm not sure what triggers this, but I experimented some with a friend, and it turns out that in the chat on the server it says "X: Checked out." when in reality, they're still in their condo. After this happens, the people on the server can still see the people in the condo chat, but not vice versa.
Here's a screenshot of it happening. Nathan did not actually check out of his condo here, even though that's what it says. The condo also disappears from the lobby doors when this happens.