that's the thing there doesn't seem to be a single focus modeVideo capable cameras generally offer you the choice of single auto focus, and continuous auto focus.
I always use single auto focus, as the camera will hunt in and out of focus on continuous auto focus.
This is what's happening to you.
Check your video settings and change it to single auto focus.
I had a look at the manual and you may be right.
There is face tracking, make sure that's off.
Can you use manual focus with video on this camera ?