@Meraidd This is, unfortunately, something Origin does from time to time. I don't actually know whether it's a small glitch, perhaps due to a file getting corrupted, or a deliberate anti-piracy measure. (Imagine installing the game on a friend's computer and then letting them play indefinitely. EA definitely doesn't want that.) Either way, once this has happened, all you can do is sign in again and let Origin verify your ownership of your content.
One thing you can try, the next time this happens, is telling Origin to repair the game. I don't know whether this requires it to update as well, but it's possible you'd get the repair first, and the update would follow afterwards, which you could cancel.
If you launch the game from its exe while your computer is offline, Origin should recognize the lack of connection and put itself in offline mode. This worked fine the last time I tried it. Origin might not load properly, but to play Sims 4, you'd only need to sign in before the game started to load. This does not work, however, if you've cleared Origin's cache: your login data is stored there, so you'd need to go online at least once after that to allow Origin to retrieve that info.
