June 2020
Is anyone else having the issue that when in build and buy mode, if you place an item it either disappears and doesn't reappear or it disappears for a minute and comes back. I've had to place items several times to get it to stay placed. I don't think my game is lagging either but it's really annoying when you build a lot in the sims and have to wait to see if your object will show. I also have an issue with painting walls. I will place the paint and it disappears in other places.
June 2020
@FilthyEarthenBoy Please repair the game in Origin: open your game library, right-click on the Sims 4 icon, and select Repair. If that doesn't help, clear Origin's cache:
https://help.ea.com/en-us/help/faq/clear-cache-to-fix-problems-with-your-games/
restart your computer, and repair again.
If the issue is still present, please test in a clean Sims 4 user data folder. Move the entire Sims 4 folder out of Documents\Electronic Arts and onto your desktop, and when you launch the game, a clean folder will spawn with no content. Don't add anything to this folder yet; just start a new save, go into Build/Buy, and see whether the issues are still present. Let me know either way.