Standing in certain places and looking in certain directions causes several chunks of the terrain to not render on the side of the screen. In minor cases its as small as it is in this screenshot. In major cases half the screen will be missing. This happens often enough for me to make an issue of it here, I run into it a couple times a day and its very noticeable when I do.

This particular one happened on a chunk boundary, I'm not sure if they all do this is the first one I've paid attention to. But I was able to stay in the chunk and follow the chunk boundary to the south and the chunks to the west of me were always unrendered.