Parts of the floor and major parts of the environment on missions are missing so much so that I rely on other players to traverse the maps. When I started plating this was not like this and i noticed it about 5 days ago.I am not sure its the graphics card but don't think it is cause it worked at the beginning.
You should still read the Technical Help sticky. Try the suggestions that are there, if those don't help you need to provide us with more information.