Sim went back in time

I did save after the glitch happened but not between returning to the lot and entering CAS.

So the series of events was: Returned to lot, did a bunch of stuff, aged infant up to toddler, went into CAS. When CAS loaded, I noticed sim had reverted to infant. Closed CAS to find time had rewound. Saved game on a secondary save slot, reloaded secondary slot to see if that would fix the issue- it didn't. So I just replayed the whole day again, saved on the second save slot again and exited.

It might be worth noting that I entered CAS through the Simology tab so if I remember correctly, I think CAS loaded before the "age up" action was fully completed- meaning sim had changed to toddler but the full age up animation hadn't fully played yet, if that makes sense. I'm not sure if that caused it but that's the only thing I can think of that I may have done differently.