Ah! SeaUnicorn,
That sounds like it might be the problem. I don't use cheat codes as a matter of habit, but, I did cheat right at the start as I wanted to use a sim I had made previously for another game, but I wanted to change her lifetime wish for this game and couldn't be bothered to re-create her in CAS. (Yes, I know I could have saved the sim in CAS when I first created her, but I didn't think about it at the time.)
Thank you MoMoll, for your suggestion, but when I said I had been scaning from 8 pm onwards, I meant that I was scanning more or less all night with my game running on normal speed.