GPU Profiling - Clear Scratch Cubemaps & Compute Average Brightness - High ms

I’m creating a level with a large 4k*4k landscape and I’m in process of optimising it as best I can.

In the GPU Visualiser, there are some processes that I can’t find any reference online too.

Clear Scratch Cubemaps 3.82 ms
Compute Single Average Brightness From Cubemap 4.17 ms
Compute Diffuse Irradiance 4.20 ms

These three processes happen before the scene rendering and total 12.19 ms

Any ideas what settings effect these values ?

Do you update reflection captures every frame?
Is your SkyLight movable?

Movable skylights must be manually refreshed via blueprint, and even then are very cheap to update, and it is completely impossible to update reflection captures AT ALL in all versions of unreal 4 without potentially heavy engine modification (Unfortunately).

My reflection capture and my skylight was Stationary. I’ve set them to static and its brought the frame time down about 3ms. I think you’re on the right track, with it being to do with my skylight, reflections ect. Maybe it’s normal to be quite large performance hit with a big scene ? Thank you for your help.

Reflection capture mobility has no impact on anything.