Hallo,
I also experience the problem of invisible materials/textures screenshot
on that image you see object with and without textures. This are simplest pbr and diffuse shader.
And I am not agreed with old GPU issue because I have brand new GPU (rtx 2080) and in my first version of that project all materials were loaded.
I use firefox and chrome latest build on Ubuntu 19.04. On both browsers the materials are invisible and I ve got a headache. Greetings ;)