Landscaping Grass, Tile, Etc. Disappearing after save and exit.

@Ligulas

Look here. This is an old report, but in this case, the "No Blu" mod was responsible for this error.
https://answers.ea.com/t5/Bug-Reports/FIXED-Terrain-Paint-Disappearing/td-p/3628459/page/2#
In your case, it may be another mod of this type.
1. Move the mods folder to the desktop.
2. Find and delete localthumbcache.package file in the game folder. Delete also all folders with the word "cache" in the name - important!
3. Fix the game in Origin.
Origin/Library - right-click on TS4 - option "Repair game"
You have to wait until Origin will fix all packs, not only the base game.
4. Turn on the game to create a new, empty mods folder and check if the game is working now properly without mods
5. Check if there are new updated versions of the mods and CC you are using.
Then copy from desktop your mods and paste it in the new mods folder. Paste script mods one by one every time checking if the game is OK.

I don't work for EA

@Ligulas

If it will not work:
Start a new test game to check if you get this error in your new save and in every world.
This could only be a Sulani bug. But you need to check if this error will be in your new game and in every sim world because it could be that only this your save or the only plot, where you are building now is bugged.
Save this new game by the option "Save as" to easy delete it.
By the way, are you on PC or Mac?