This is a stupid bug report. If you don’t know already, the new materials are in “Beta” and I am sure you know that anything in Beta will not be shown in game. So either wait for them to come out of beta or just upload it yourself? (Basically what the post above me said, I didn’t read it.)
When ever you find these kind of issues try using a 3rd party plugin works allways faces same issues few years ago
or try importing a mesh with texture WORKS!