Thanks, I was actually hoping this was a common enough occurrence that someone could easily point me to a solution. I noticed a couple of other people mentioned problems with landscape segments not rendering and the solution was simply to select shared wrap on the textures.
Anyway I figured out in the meantime that my grass blend layer was the culprit. It was counterintuitive because the grass layer worked fine. I was blending two sets of textures and varying the blend on view distance, plus macro variations and heigh outputs. In the end I got rid of everything except one set of grass textures and the problem went away.