Only the very reflective materials. I tested to see if the Steel material from the Starter Pack is affected as well and yes it is. The textures have basic configurations, I tested them in another unreal project and they are fine. I think it has something with the rendering settings, however the Project settings are the same to any other unreal project I have. I changed each and every setting just to check if the problem can be erased but unfortunately it didn’t work.
I noticed that when you move the camera, some sort of grain effect moves too. I disabled the grain effect in the post processing volume but the problem still persists. Apparently it happens only when the light barely hits the surfaces. When you place the meshes to a light source, the problem disappears but when the mesh is in a shadow-ish place, the strange phenomenon activates again.