I was shooting skateboarding today with my new 24-70 2.8L and everything was going fine, but I started to realize after a while that every time I was shooting portrait style the camera had AF issues, like I'd press the button and nothing, I'd try half pressing 4 or 5 times on the subject before I pressed fully, and I'd see the red box, but no click, no picture, but it was fine shooting landscape. I was shooting AI servo with center point focus. I know it wasn't the lens because I also tried my 70-200 f/4 and again, fine in landscape, horrible in portrait. I'd say one in every 5 shutter presses actually took a photo.
Any ideas? Camera is not gripped.