I was using Darktree but I figured out a better way to get around it. For a planet, just render out the material on a rectangle then apply that image as a texture onto a sphere.
I figured out what was wrong. One model was "corrupted". Apparently, the program doesn't like rendering 2 patches that can easily be combined into a 5-point patch.
But anyway, finally! I was able to render my image today. It took only 20 mins! lol