+ I just noticed that if you load that same CXR back into the VFB to resume rendering that all of the lights get messed up (What was previously the light on the left is now the light on the top, just really messed up order of things).
It however only happens on "first load". If you've rendered the scene, played with lightmix all in the same session then the lightmix will work as intended again.
It is a different issue than the OP but kind of similar so I posted it here.