Product: The Sims 4 Platform:PC Which language are you playing the game in? English How often does the bug occur? Every time (100%) What is your current game version number? 1.110.294.1020 DX11 ...
Ideas
Sounds like something else is wrong with the lot. Do you have endless loading only when uploading to the gallery ? How big is it ?
Do you have any other lots you have this issue with (the items disappearing when placing, not endless loading). It's best to keep this thread on topic so maybe make a new one for the endless loading.
Here's some troubleshooting steps you can try beforehand: https://answers.ea.com/t5/Game-Issues/PLEASE-READ-Crashing-and-Endless-Loading/td-p/14171320/