1/125 is too slow to stop movement, if it's candids, not posed "hold it" pictures, you will get blur.
It could be that Auto is also setting the ISO, or that what was in the scene changed, maybe more light from the background.
Using f/2.8 gets you more light, for a shorter shutter speed, but less DoF which makes the focus critical.

I guess that most of the problem is motion blur and camera shake, not focus.
Can you post some examples?