Hi,
So after a bit of playing around I discovered that the problem might lie in the exported Archicad geometry itself.
I’m attaching a new rendering, where I made the geometry in Twinmotion itself, applied same materials, inserted the same tables, vase, the sofa from the library…The opening is not empty, there is a thin plane with the exact same default Clear Glass material applied to it.
So I just saved myself few hundred moneys that I don’t immediately need to spend on new hardware 
going to focus on proper/correct Archicad exports for now…
