There was a bug in the VMF Exporter when using the Concave Brush option (and potentially with CorVex) that was fixed in today's update to WW. This bug would make the viewport stop updating after exporting a scene to VMF when any objects were tagged as Concave Brushes. This would also make the scene unresponsive and lead to a Max Crash if you tried to edit object transforms and add scene nodes after the export.
Download the latest WW (2.04) to patch this bug.