I just purchased a 5dM4, and think I am observing a peculiar issue with banding in exposure times over about 6/10's of a second or more.
A prominent horizontal banding displays that can not be seen on shorter exposures, like 1/30th of a second.
To most easily visualize this, I took two dark frames, one at 1/30 and one at 1 second. In Lightroom the only alteration is set the white point clipping to the same value for both exposures and turning off NR & sharpening for both exposures.
Is any one else seeing this horizontal banding? I am not expecting perfect shadows, but this is surfacing on exposures around a second and greater, and not on short exposures.
This problem notwithstanding this "brickwall test" is showing up in more normal edits too, places where my 5dM2, with its not so great shadows seems to be better than this issue, as this banding appears to be large streaks of chroma.
I tested this out dark frame scenario on my older 5dM2, and the results while different, are not this dramatic.
Note I resized these to 1024px wide to keep within the file size attachment restriction.