1) What gerber viewer are you using? It may not be rendered 100% accurately. For example, gerbv has 3 modes: "fast", "normal", "high-quality". If you choose "fast" or sometimes "normal", you can see artifacts like this that disappear in "high quality" modes.
2) If you created the regions by juxtaposing tracks, try overlapping them a bit more. It will make no difference in the PCB, but will cut down on the artifacts due to inaccurate rendering.
3) From the triangular void in your picture, it looks like the tracks are not all entirely parallel. Perhaps some are 1 or 2 pixels off from top to bottom. You can edit each track and check the X and Y coordinates of the endpoints, and fix. Again, no real impact on the PCB, but may contribute to this artifact.
4) Why not just draw the outline of the region using primitives, then convert to a polygon. Then you can control the resolution of the arcs as well. Also, it will result in a smaller, quicker rendering Gerber.