[Lost walls, all slabs, and roof in all rendering modes]

I just had the same problem, and went through the advice suggested above, with no luck. Then went into the 'edit wall style' dialogue of affected walls and that seemed to reset the issue. Nothing was changed in the wall style, but the wall styles all refreshed when OK was selected on exit.

[All 3d Geometry in all Files Turned Black]

Just had this problem too!

 

Was checking for stray geometry/objects by using zoom to objects for each design layer. 1 layer went incredible wide and turned out that a windoor object had ended up kilometers from where it was supposed to be. Once deleted everything went back to normal