Earlier today, there was another PC that downloaded the Sims 4. This PC's Microsoft/OneDrive account is under my email. As a result, when this PC downloaded the Sims 4 on their PC, all of my progress on my own PC is gone, just because both PC uses the same email address under the Microsoft/OneDrive account.
cedgori Installing Sims 4 on another PC shouldn't have deleted your data even with both systems linked to your Microsoft/OneDrive account. But maybe something weird happened.
Do you see the progress from the other computer on your main one, as in, new saves or households? On the new computer, is it possible that Sims 4 itself was installed into Documents? You can check in the EA App, under Sims 4 > Manage > View properties.
Please also let me know if onedrive.com has your old saves, either in My Files or the Recycle Bin, perhaps renamed (and therefore not usable by the game) but hopefully still intact.
