Lines disappearing parcially, what could it be? It suddenly vanishes without editing any settings.
Looks like issue with your graphic card or its driver. Check that you're using a certified card or tested driver. Also run SOLIDWORKS in OpenGL mode (you can do that via Rx tool) and then see if the issues are still there. If yes then it's a graphic issue else report back to your VAR.
I have the same black behavior when I opened my assembly saved to parasolid (xt)
Problem is solved by using original SW part template
Retrieving data ...