I wanted to make a quick post about an issue that I was having yesterday and the solution I found - in case this is interesting to anyone else.
One of my VP goals is to be able to tightly integrate the live action into virtual environments and Ray Traced Shadows are an essential deal to this. Previously, in long-past UE4 versions, I had no issues with casting a nice raytraced shadow from the billboard but in 4.27 I could only get a solid black, full coverage shadow from the entire billboard (a big black rectangle!)
Some fidgeting around and I could confirm that Shadow Maps could work but they're so awful and I wanted to pursue this as I'd done this before with success.
Searching the forum here I found several topics near to the concern but not solid solutions/anything that could work for me.
I ended up building a diagnostic scene to test it and found that the default "Translucent" blending mode indeed casts only a solid shadow without considering the Opacity plug. "Masked" mode works so I hacked into the "Billboard_lit" and "Billboard_Unlit" master materials and changed a few parameters and found that this worked!
Translucent Blending Mode,
Clipped Blending Mode,
Material parameters I changed.