On a heavily used Nikon D750 w/ AF-S NIKKOR 24-70mm f/2.8G ED:
When using live vision, ussualy while holding the camera up over my head, autofocus focuses nowhere. This happens right after having shooted a correctly focused photograph using viewfinder, with slight subject distance variation.
When doing so, I hardly ever want a shallow DoF, as I'm focusing on groups of people, so F-number is always between F5.6 and F16. Focusing mode is AF-S-wide at center point, and I don't use shutter button focusing, I use only dedicated AF-ON button focusing. So it should just focus at center of image as I press AF-ON button, and keep this focus distance until I shoot.
On this example, it seems to be getting stuck at its shorter focusing distance:
On this subtle example, it fails to focus the central situation, setting focus on closer, peripheral subjects (as if I was using multiple point AF selection, what I am NOT doing):
(f/7.1, 1/125s, ISO-5000, I pressed AF-ON button while pointing to people speaking at the table. Zooming in image shows that the focus is set on the heads of the people close to the camera, speaking persons are completely out of focus.)
Is this caused by a fail, A D750 common issue, or a mispractice?