@Modphex: Thanks for the feedback for this game. Neither official builds (for UE4 games) nor specific builds from me doesn't include any materials related info to gltf export, though in specific builds referenced materials are exported separately along with textures similar to psk export. It's the same for animations, in any build animations can be exported to gltf only with the mesh, there is even respective warning in logs while trying to export an animation directly from tree view.
It's also worth to note that most clothes in the game, instead of diffuse/albedo textures, are painted via masks and respective material properties applied on it. And some textures are virtual ones. For general limitations and possible issues please read
this topic.