The problem seems to be that the LightComponent on a DirectionalLight actor has someone become invalid or null. I’m afraid I can’t think of any way that could happen, it could just be a corrupted file. If you are building the engine yourself, you could try changing the engine code in that function (ADirectionalLight::PostLoad) to check GetLightComponent() is non-null before accessing it, but you may find it crashes somewhere else. As you say, the best solution might be to roll back to an earlier version in revision control. Please do let us know if you see this again, or even better, if you have reproduction steps.