ok, I think I got all the screencaps you suggested. That was a good suspicion but alas it was set to "Surface Opacity"Can you show us screenshots of what you ARE getting out of LW 2018.
What I'd like to see is the following:
a) scene's viewports that show all the objects in the scene.
b) Image viewer's final render and alpha buffer render.
c) The surface editor. One with the Material Tab and One with the Shading Model Tab
My suspicion is that the Shading Model Tab's Alpha Channel option for each surface is set to Unaffected by Surface and not the default Surface Opacity but until I see the screenshots, I won't know for sure.