Forgive my ignorance here, but can this issue just cause unexplainable oof images? I've been shooting a lot with the 24-70 lately, and it is perfectly afma'd, but often I aim at something and it just won't focus properly. This sounds nooby, but it's not "the occasional oof iimage" I just doesn't focus right, and not in front or behind, it feels like it just doesn't even try to get it right.
How was it "perfectly afma'd?" What you describe (neither front- nor back-focus but still a soft image) sounds like a problem with the lens, e.g. decentering. What do shots taken with Live View AF look like?
I used Reikan and tested nearly 2000 images, plus that I have afma'd all my other lenses over the past 5-6 years to hit dead on, and the 24-70 also hits dead on most of the time, equally sharp on both edges and top to bottom, EXCATLY the same sharpness with LV and phase.
And I might have put that a bit wrong, because when it's oof, it must be either back or front, but it's off by 2 meters at 2 meters so it's nothing to do with afma, it misses by (nearly)the same distance I shoot often. But it's the ones that are far enough off that the images is completely useless and not by so much it shows in VF or the dot blinks telling me it can't find focuses that are causing me the issues.
Here's just a on the fly typical missed shot. The point is on his head.
Usually they look like this:
ps, I know the light is QUITE different, but the problem is random at any type of light.