Sorry to hear that. I thought the problem must be with the AF sensor --- but in your case looks concerned with lens ...
Could anyone explain why lens could lead to OOF? I guess some glasses were shifted so its focus range become too close?

Does Anyone have a solution to this problem? I have the same thing happening in my 550D, I google it and found this thread.
Please, using liveview mode to focus is horrible, too slow. These cameras were designed to be used in the viewfinder, not in thew live view

This problem drives me crazy.  I see it on about a third of my shoots.  I see it more on my 50mm 1.4 & 85mm 1.8 primes, and not as much on my 28-70mm 2.8.  (Yes, I do like the difference is shooting lower than 2.

And, for some reason, if I change lenses in a shoot, it seems to only affect one or the other.  That has been my method to fight with this issue, although it's not foolproof.

I also have tested this and found that shooting up close (3-5 feet) is no issue.  For me, it occurs at 10-15 feet.