Sony a7xx face detect issues

[enerlevel]

hi all,
I have a Sony A7s II along with 28mm f2 FE lens. Both are on their latest firmware.
I am having issues with face detect focus... I use face detect On , focus wide.. the camera detects faces with a green box but none of them are actually in focus..
For example I had a couple stand against a wall. As usual the green box was on their faces but when I previewed the pic, the wall at the back was in focus. This happens 80% of the time. I sent it to Sony but they said nothing is wrong with the camera...
Center focus and eye detect works 100%.
Is anyone else having these problems? Also aperture and light seems to have no effect. If I use higher F stops, still faces are blurry.. and happens during the day as well as low light areas.