As you can easily mimic that effect in Unreal Engine by not baking your lighting after you expand the size of your world, it’s very much likely it’s related to lighting.There is a post processing node which would probably have the lighting bounds, but i’m sure you’ve already looked at that, or the Skybox could have the lighting bounds as well.
If there is no Light baking in the ADK they would be computing the lighting each time the maps were loaded.