-Floors will never be shown on floors above the first one, you need to add blocks. The engine is NOT true 3D in this regards, it works more like Doom engine - with 2D maps and 3D rendering.
-Entities should not disappear. I'll ask my tester to check it.
-Audio settings crash bug is hard to reproduce. I don't have such a problem thus I can't fix it. Only chances are for my PC going haywire and reproducing it for me.
-Enemies duplicating should be fixed. Check if you're on the last version and not experimental one.
-It will always be there while testing.