When I use SceneColor in a translucent material separate translucency does not work. I can’t find any information on whether this is a limitation or not, except this answer hub question about SceneColor and separate translucency in particles. That question is similar to this one, but issue UE-15433 states that SceneColor breaks Separate Translucency for particles when SceneColor is used. This is probably the same issue, but not with particles.
If I don’t use SceneColor for the transparency the material is opaque and seems to work (not affected by post processing).
However when SceneColor is used the material is affected by post processing, even though separate translucency is enabled.
Underneath is a mock of what it is supposed to look like
