Operating system: Mac OS Mojave 10.14.4
Graphics card: Intel HD Graphics 400
Broken: blender-2.80.0 f0ybdd7c9c4 2019-05-13 22:40
Short description of error
In general Blender 2.80's Principled BSDF should interpret transparency using its new Alpha slider instead of its transmission slider. In the attached example you can see how the use of transmission instead of alpha gives the model a glassy look. Plugging the opacity texture into the alpha slider instead of transmission quickly solves the problem. Blender also uses Roughness instead of Glossiness. Therefore, by default glossiness textures should have an additional "Invert Color" node between the image and the roughness slider.
Exact steps for others to reproduce the error
All that is needed to reproduce this bug is to open a new start file. Use "File > Import > FBX" and select the attached "Walking.fbx" file. All of the imported textures use Transmission when Alpha should be used. I've noticed that the same issue exists with OBJ/MTL files however an example is not attached for this case.