I went through three copies before giving up on the 24-70mmL f/2.8. Awful!
It's more often than not, the camera body and not the lens that's off.
I agree 100%, check the camera body well before jumping to conclusions about the lens.
Thank you, yes, I was aware of this. It is my enduring good fortune to live 10 minutes drive from our regional CPS where I am a Gold Member. Tests, repairs and calibrations were done on lenses & bodies ad nauseum. It was just breathtaking bad luck that my three copies of the 24-70 f/2.8 were lemons. I have to say in spite of the outcomes, Canon CPS were very good about it.
Typically there would be a zone of very soft focus across 20% of the frame, right in the plane that is in focus. So for example if you did the "brick wall" test with everything perfectly squared up, there would be a soft "band" through the frame. Punishing and professionally unusable. Think group shots...
My other eight Canon lenses are all perfect matches with my four current working bodies. Trust me...it was the lenses.
Do a search or read older threads. For the fortunate few there are positive experiences, but the prevailing reality is that 24-70 f/2.8 has been an irritating disappointment to plenty of photographers.