[FIXED] Random items, landscaping, terrain paint disappearing from build

Product: The Sims 4
Platform:PC
Which language are you playing the game in? English
How often does the bug occur? Often (50% - 99%)
What is your current game version number? up to date
What expansions, game packs, and stuff packs do you have installed? all except My First Pet Stuff
Steps: How can we find the bug ourselves? I have a lot built in Sulani uploaded to the gallery (Sulani Paradise Spa), and you can try placing the lot and loading/exiting/loading the lot over the course of gameplay.
What happens when the bug occurs? Items are vanishing en masse from this build. I first noticed that some random items did not download with the lot when I placed it into other saves from the gallery, and now I'm noticing that when I go back to the lot in one of my saves, more and more items are vanishing. Some items that have vanished: chairs placed at tables, indoor plants, outdoor plants, and most oddly, all of my terrain paint seems to have vanished as well. No CC was used while building the lot, and I disabled CC while finishing and uploading the lot to the gallery. This started happening with no mods/CC enabled.
What do you expect to see? I build a lot, upload it to the gallery, and when place it in the world, it has all the items used in the build. Also I expect that items/terrain paint do not disappear between visits to the lot.
Have you installed any customization with the game, e.g. Custom Content or Mods? Not now. I've removed them.
Did this issue appear after a specific patch or change you made to your system? Yes
Please describe the patch or change you made. This is the first ground-up build I've done in Island Living, and I haven't personally seen this phenomenon before.

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As described, items are vanishing for no apparent reason from a spa I built in Sulani... Even terrain paint is missing. It's a large building with a fair number of items, but I've had large, complex builds before that haven't had this issue. I do use MOO, but some of the things that disappear were not placed with MOO (chairs at tables, for example... and the terrain paint). Really frustrating. I put a lot of time into this build. 😢

When placing the lot from the gallery, there seems to be a good chance that not all of the items will load, even though they are visible in the gallery preview. But it's stranger to me that every time I visit the lot, it seems that something new has vanished.