Depending on the camera, all the day/night switching does is uses one profile and simply switches from color to IR and B/W.
So in the business settings that Dahua caters to, the same settings for shutter, etc. can be the same. But for a house where it will be a lot darker at night, using one profile is problematic.
So probably what you experienced is snow or full moon or something that provided more lighting that allowed it to "work" some of the time because it was using day or general profile.