I apologize, as I recognize that this is not necessarily a question. This is more of an answer to a bug report that exists on the issue tracker.
Bug Report: UE-116954
Note this is also for UE 5, which I recognize to be early access. I just don’t want people to be turned off of playing with Nanite because of this odd behavior where a Sky Light set to stationary (which is the current default!) causes various Nanite meshes to decide to swap materials at runtime.
For those having this issue:
Turn your Directional and Sky Light to Moveable and then just reselect all of the static meshes in the scene to fix the swapped materials
(Changing the Sky Light to Moveable with meshes already in the scene causes them to have swapped materials in editor, but not runtime, oddly enough, until you literally just click on mesh instance. Reloading the editor may also help, but I did not test that.)