Hi!
I think I've found what causes this bug - it's apartments (including the ones we build ourselves with the "For Rent" add-on) and penthouses. If a person plays only on regular lots and does not visit the apartments and penthouses, then he probably will not have a problem. But if you play in apartments, you will have this bug anyway.
And yes, sometimes they are quite difficult to detect. After checking all the neighborhoods in which I have rental housing, I found flying objects in all of them. Sometimes I had to move to the very edge of the map in Tab mode - from the game area they were not visible at all.
In general, ordinary lots normally coexist with interactive objects on the inter-lot space, but in apartments / penthouses they are duplicated for some reason in Zone Object Data (that is, in the part of the save, where ideally stored data only on the objects placed on the lot itself), after which the game catapults them high up.
And this is clearly a game problem. Perhaps the release of the "For Rent" add-on exacerbated this bug, and now flying objects appear wherever you place apartments. Also any interactive object on the interloth space can fly away: plants, collectibles generator, snow drifts and piles of leaves, bicycles, plates from which the NPCs eat and so on.
I discovered this while editing the save file through sims 4 studio, as already written here.
On the attached screens show these objects with some crazy coordinates (for comparison showed and normal objects placed on the lot). I deleted them, and the flying objects disappeared from the save! But this, of course, does not save from the appearance of new ones.
Maybe this information will somehow help the developers to solve the problem.
(I'm using a translator to write here in English, but I hope it's still readable 🙂 )
