Rect lights cause visual noise on the light rendered when using raytracing. It is easier to see when you get rid of all other light sources in the scene. I have attached an example project.
This seems related to UE-68247.
Found in 4.23.1. CL#9631420
Reproduced in 4.24 P1 CL#9979423, 4.25 Main CL#10098181
1. Create a new project with raytracing enabled.
2. Set RHI Default to DX12 and enable raytracing.
3. Restart the project.
4. Place a sphere and a cube in the level.
5. Place a Rect Light next to each mesh.
Expected: The light renders properly
Result: There is visual noise in the render.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-84274 in the post.