I found an issue where if I try to lower the sun below what I am guessing is the horizon, the sun won't represent that translation.
For example I have linked the sun to its target, and in the first image below, the sun is in a defualt orientation near the horizon. In the second image, I have rotated the sun 5 degrees in elevation above the original location. In the third image, I have rotated the sun -5 degrees below the original location, and it doesn't look like it has moved the expected amount. Then in the fourth image I have rotated the sun -10 degrees below, and it looks lilke it is in the same position as the previous render.
I need the sun to be able to go lower than the horizon, as the scene I am working on takes place in the sky, and I want to simulate the natural movement of a skyship by gently rotating the environment HDRI and sun, instead of having to rotate all of the geometry, cameras, lights, etc.