I've never used materials in GZDoom before so I'm probably doing something wrong but I have a PBR bullet model and in Blender it renders properly but in GZdoom it doesn't. In GZDoom the model has a weird blueish-green color and doesn't have any metallic properties. I have a normal map, ao map, metallic map, and rough map, I've placed them in the auto materials directory, so I'm at a loss to explain what is not working.
A couple of screenshots:
I've prepared a simple example demonstrating my problem. Load it up and summon "Test" to spawn the model. I had to use my Dropbox as the file is too large to be an attachment, this is because the model's texture and maps are all very high res at 2048x2048.
https://www.dropbox.com/s/ms52dm7o83bzpew/Test.pk3?dl=0