Canon Mark III focus

Been shooting as a pro for 25 years and this is the first time this has happened so im thinking its a setting but haven't been able to find it. I shoot sports with the Mark III and the camera has been pulling of the subject and focusing on the back ground, or another close subject mid way through a progression of shots. I tried it with a couple of different lenses and it did it with both. Both nice 2.8 glass. Cant seem to figure it out, played with a bunch of Custom Settings and cant get it to quit. Any help would be appreciated. T