I just migrate asset from Reflections demo, but I have really strange shadows. I didn’t change mesh settings, so what’s wrong?
Increase the lightmap resolution of your ground 
This would depend on how large your ground surface is. If you have a large ground surface you’ll need increase the LM resolution. If it were a smaller mesh you wouldn’t need to increase it nearly as high.
To get sharper shadow, use dynamic light as stationary or movable