So I've been digging around in engine and online for some techie stuff on Lumen. I had to ask on the UE dev forum to get a clear answer, but there's at present no solution to completely fix Lumen's reflections issue. Here's a screen of the answer I got: I used the CVar that suppress the noisy lumen reflections in my scene.…
You are seeing artefacting from the Lumen ray tracer trying to denoise/resolve detail with limited information. Not much you can do about this except increase the number of samples and/or increase the intensity & size of your lights. Does your graphics card have hardware raytracing? The lack of mirror reflections are odd,…