Just started playing around again after my hiatus, and running everything on 127.0.0.1, latest GIT, Debian/Testing, QT5.7. ATI OS drivers. (Just on spec, I tried with QT5.6 too but same deal )
When I start up the interface, everything (avatar from Mixamo, mesh from Marketplace, cube created locally) flashes briefly with its colour/texture as it loads then goes black.
Popped across to another (external) domain for a moment and had same issue.
Above: Ready to host MST3K