There's nothing in COS or COR that would control this.
Are the phones programmed for the same COR for day, night1 and night2? If you have a console, the default COS will log it out after 10 minutes if there is no activity on it. This can change you from day mode to night mode and if your COR is different it could be blocked.
What exactly are your symptoms? No dial tone? Locked keypad? Completely dead?
What, if anything, do you do to bring it back on line or do you just wait a while and it starts working again?
Ralph