I’m using instanced static meshes in my project, and noticed that when I spawn in an instance scaled on an axis by a negative number, the object does not retain sensible normals while flipping, as happens when a negative scale is applied to a static mesh in the editor or a static mesh component is spawned in via blueprint with a negative scale, but instead flips some of its normals, creating issues where lighting is incorrect and camera-facing faces are not drawn while backfaces that should not be rendered are drawn.
I created a blueprint to test and verify this bug, which can be seen below:
Here is an image of the bug as shown when running the above blueprint with the default sphere mesh being used as the input mesh and the default material being used as well. In this scene, shown is a row alternating between flipped and non-flipped meshes. I have tested this bug with my own assets, and noticed it occurred in those cases as well.
Here is a normal buffer from the above shot:
Tested on a Windows 10 machine running an Intel 4770k and a Nvidia GTX 1070.