I have a problem with solving this problem, the shadows before they left correctly, but changed suddenly and now look wrong. In a new file they look good, but when importing another file they change without reason. I can not remove divasunpath from the display options, uninstall trying to fix this error, but it is not completely removed from rhino.
If you get your file with the correct looking shadows, then import another file of some sort it changes the shadows is that correct?
When you hide the object you just imported, do the shadows ‘fix’ themselves again?
If yes, something in the file you imported is pretty far from the origin/ center point of your model. Keeping geometry close together may solve your problem.