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.