Rect lights + RTX GI + Hires screen capture

Both of these images were captured using “High Resolution Screenshot” in UE4.27. All lighting is dynamic. The only setting difference between the two is in the type of RTX global illumination. The darker one with no light in the upper slats is using final gather. The one where everything is illuminated is using brute force. The lights that are changing so dramatically between the two are all Rect Lights.

Is there an explanation for the very significant difference between the two?