I'll also suggest it is implement drift.  I had a real eye opener a few weeks ago.  We are ridge till and run a 16 row mounted planter.  We've been using RTK and RTX for 15 years but as our equipment has got bigger we've struggled more and more with guess rows.  We thought we were pretty good this spring but I put a GPS guidance hitch on the cultivator a few weeks ago and it is doing a lot of "fixing" of ridges that are off by a little bit.  It hasn't taken out much corn but there are a lot of places where the old ridge is off by 2 inches and the hitch moves the cultivator to the right place.  I used to laugh at all the guidance hitches and guidance discs but I'm a believer in them now.