I also have noticed this problems with doors where the bottom edge coincides (intersects) with parent surface bottom edge. The way I solved the problem was to edit the osm file with a text editor, slightly increasing height of door bottom edge (modifying the Z coordinates). After reloading the osm file the lost subsurface now reappears in Sketchup. The reason for the problem might be rounding errors in Sketchup or OpenStudio plug-in.Sketchup.

I also have noticed this problems with doors where the bottom edge line coincides (intersects) with parent surface bottom edge. line. The way I solved the problem was to edit the osm file with a text editor, editor slightly increasing height of door bottom edge line (modifying the Z coordinates). After reloading the osm file the lost subsurface now reappears in Sketchup.coordinates).