try making materials two sided, or double checking again in sketchup using the style panel and the button for the the white/blue ish swatch. Previous versions were much more permissive with thin or infinitely thin materials being one sided and auto normaling them, but I think the update intentionally broke that. It can be time consuming but its easy to fix. If that doesnt do it, save a copy of your SU model and group all of those chairs and tables and then explode them a bunch, double check the normals show the white default material then jump back to TW, update to the new file reference and then double check that material (use eyedropper) and make sure it has double sided checked. It will very likely resolve your issue.