Crash in FShadowSceneRenderer::AddDirectionalLightShadow

This is a race condition between the FShadowScene update & rendering, where sometimes the renderer tries to access a data array before it has been populated leading to the crash. It happens fairly rarely because a number of conditions have to be met. For example, in editor the race appears very difficult or impossible to provoke (even with instrumented code).

However, it is not impossible for it to become a common for certain games if the right conditions are met (adding a largish number of lights on a given frame, including a directional light).

Note the ticket FORT-916328, showing the crash is occurring in FN live.

None known, see linked crash reporter cases