The way consoles work is this: if only one console is logged in and the only active console operator logs out, it puts the system in Night Mode automatically. You can then over ride by putting the system back into day mode without logging an operator in.
If two consoles are logged in it does not do this. (No way to change this.) So if console 2 is not logged in the system will go into night 1 automatically.
If, however, your users insist that both operators are logged in when this happens, check for two things:
(1) check the COS of the consoles for the inactivity timer. Default is after 10 minutes of not making or taking a call, the console logs off. Your second console may be idle for longer than that.
(2) Watch the operator of console 1 log off to verify there isn't something she is doing to cause this.
Ralph