I've noticed the "RT reflections" they introduced with the latest patch specifically on bodies of water isn't really RT but SSR. I asked the devs through Twitter but as expected was met with silence.
"Raytraced Reflections have been enabled on bodies of water, including the Black Lake."
Either it's broken or someone forgot to push something through to enable it.
The latest game update fixed a lot of bugs but the issue is Unreal Engine has deep seated issues that Epic refuse to fix.