Terragen 2.1.18.1 crashed on me when I deleted a node in the graph while performing a render. I can't immediately reproduce it, but I was messing around and created a Rock node (not a population), focused the camera on it, assigned an Alpine Shader to its displacement function (which produced no reasonable result), a power fractal to its color function, and then deleted the Rock node itself mid-render.
Regards,
Shane