I had a similar experience when I got my 6D2. I went out in front of the house that night and shot pictures of the blooms on bushes with only the light that spilled over from the front porch and from the light down the street. Everything was set to "Auto." The blooms near the front are very sharp and the color was not even that bad at ISO 40,000. Of course it was noisy as all getout, but tamable in Photoshop.