@Leyira I don't know why this happened and can only think of two plausible explanations. The EA App temporarily budgets extra space when repairing a game. If your computer is already relatively low on free storage, the repair could have triggered OneDrive to push your files to cloud storage only, and then either the sync failed or there was some other weirdness with which files (or file versions) were retained. (For example, if OneDrive had previously synced saves from a different user folder, it could have tripped over the identical save names.) This is one reason I always suggest OneDrive be removed or blocked from syncing Sims 4 data.
The other possible explanation is that your game is installed into the same folder that holds your user data, and the repair removed some data from that shared folder. You can check this easily enough: open the EA App game library, click Sims 4, and select Manage > View properties. If the locations match, it's a problem; let me know if you need help sorting this out.
Other than that, I don't know, and you're not the first person to report this without any good reason for it happening. If you want to make sure your saves aren't anywhere else, you can download Everything, from VoidTools, which is a free search tool that's much better than the built-in Windows option. Search for Slot_ and see if you find anything that doesn't belong to one of your other user folders.
