Building Mode - Disappearing Items

mhoney  As a test, please try playing in a clean user folder.  Move the entire Sims 4 folder out of Documents > Electronic Arts and onto your desktop.  When you launch the game, a clean folder will spawn with no content.  (Your saves and other content will be intact in the folder you've moved but temporarily unread by the game.)  Don't add anything to the new folder yet; just start a new save, jump into build mode, and see how it goes.

If you see the same issue, please provide a dxdiag.  Click Windows key-R, enter dxdiag in the run box, wait for the scan to finish, click "Save all information," and save the file to your desktop.  From there, you can attach it to a reply using the paper clip (Attachment) icon included with the other formatting buttons.