Let’s look at the following scenario:
You have a host project containing a linked project. You copy an instance of the link and mirror it [maybe for an adjacent townhouse with a reversed floor plan]. Then in the view you turn on Graphic Display Options > Shadows > Show Ambient Shadows. You notice the mirrored link instance ambient effect appears reversed or distorted where the original appears fine.
When mirrored Revit may treat the geometry faces as they are inverted for the ambient calculation, so the results could appear different than the original.
There are 2 approaches I would recommend should you run into this behavior:
1. Temporarily Bind the Mirrored Link Instance
For scenarios where you simply need to create a presentation image or similar, I would recommend temporarily binding the mirrored link instance in the project.
Select the link instance > Bind Link. This will move the link instance into the project as a model group. This should display the ambient shadow effect as expected. Do not save the project when complete.
2. Rotate Link Instance instead of Mirroring
If you can achieve a desired result through a series of link rotations instead, I would recommend this approach. When rotated the ambient shadow calculation on the link geometry should match the original orientation link.