Sony Camera Loses focus as soon as I press the video record button

[Troman77777]

I have Sony A7II. I try to record a video, I half-press the shutter button to focus on my subject, but as soon as I press the video record button, the focus shifts slightly and the subject becomes out of focus. I focus on the face of the subject and the "focusing rectangle" is smaller than the face, so I doubt that my camera focuses on the background. It didn't happen in the past, but happens all the time now. Does anyone know what the reason is and how it can be fixed?