The 2sided materials are the materials without “_base” in their name.
They are the ones applied to the object.
2sided materials don’t really have material information, they just make things translucent. That’s why they need to reference the “_base” material which contain the actual material information (texture maps, reflection, etc)
OK I see the issue now.
You are using VRMat files. When using these, Transmutr just passes the data along and doesn’t modify it. Essentially, the VRMat data overwrites all the other parameters in the material panel of Transmutr. So even if you set the material type to Translucent in Transmutr, if you also set a VRMat file for the same material, the V-Ray material will end up being what’s recorded in the VRMat file.
If you load the VRMat files you provided directly into V-Ray for Sketchup, without going through Transmutr, you will see that they are not 2sided materials.
The materials need to be 2sided before being saved as VRMat files.
You may wonder why the other fields are not greyed out when a vrmat file is provided. This would make sense if we only supported V-Ray, but we actually also support Thea and Enscape so we need to let the other fields active.