Material's texture is missing when using xvfb

I'm using unity2018.2.6 linux version for my projects. Briefly, the problem is related to the rendering of the materials when using xvfb.. It does not work properly. On my local machine using my local X server, it works properly, however, if I run the environment on a distant machine with no display hardware using xvfb, it shows black textures.

Here is an example:

1. Local machine.. physical device

2. Distant machine using xvbf

Here is a link for full details about the problem I encountered. I'm still not sure where the problems is.. Any help would be appreciated.