Your path tracing result is phenomenal! However, I’m trying to create a real-time interactive archviz app (it’s actually my old apartment that I just moved out) so path tracing may fall short here.
After some search I think I found the cause of my original problem here.
It seems that lumen reflections rely on the surface cache it generates, and there’s a limited number of cards placed on each mesh.
In my case, the pink parts are black in the mirror because they don’t have surface cache coverage.
According to the UE doc, I tried increasing the max number of card for that particular mesh but it didn’t seem to fix the problem, so I guess the next thing to try is to separate the sink into smaller and less complicated meshes.
It’s gonna be a busy new week for me but I will keep you updated when I have any progress on this! Thanks a lot for the help!