I received a call that the elevator is shutting down twice a night (only at night) at 9:30 and 11ish. Door opens to call on ground floor. Push call button to upper floors and nothing happens (call lights up). If someone walks up and calls up and calls it it will go up. All the while blinking the ground floor button, and first floor button. After about 20 minutes it sorts itself out and begins working.
Any ideas where to start on this weird happenstance?