I recently ran into an odd problem.
To show you what has been going on, I created this bare bones version, pared down to its basics. As you can see from the attached screenshot, the problem is having part of the image missing during rendering. I say part, since not everything is affected. In this example, the entirety of the bulging, round feature sitting on the spire appears in the preview window but is truncated in the rendering.
I have attached the tgd file in case this might be of some help.