I’ve encountered the issue before without ray tracing, and I thought it could have something to do with the volumetric lightmap and its settings. Are the directional and skylight each static / stationary / movable? Is there also a Light Propagation Volume enabled (not merely in the Show flag, but for the project)? To check, go to the ConsoleVariables.ini file and look for r.LightPropagationVolume = 1. It’s set at 0, then it’s disabled. It has similar artifacts when placed over the scene…though if it’s following the camera and is at default settings, then it’s obviously not the LPV.