So I've been trying to figure this out and I can't get it to go away. If clouds have any haziness around the terminator, there is this hard shadow line that appears, but then just ends and returns to faintly glowing clouds. What could this be? Here is an example from my latest terrafromed mars, and even here I had to reduce the density of the clouds so far I lost the thickness I wanted just to reduce the shadow which caught my eye too much.
I assume it's shadow created by clouds, but if that's the case, why is it so localized and doesn't affect the rest of the clouds curving away from source?