I still thing it's the symptom of a bug. Something caused it but the lags are not the bug itself.
To explain this further. The Sims 3 issue was a broken 'alarm'. Meaning Sims in Sims 3 have alarms that tell them what to do at certain times (the inactives) and there were several issues that caused them to break. The game now tried to trigger the Sim over and over and over which made the exact same symptom show as you have now.
One bug was a corrupt outfit for a firefighter, one was the alarm clock not working properly for self-employed Sims and so on. THAT is what needs to be fixed.
I don't know how the systems all work but it's very difficult for Maxis to fix this unless they can duplicate the issue. Since it was/is not savegame based for you, I don't know what could trigger it unless all the savegame you've started have something in common (other than the Maxis defaults).
The reason why I moved your thread here is cause bug reporting is a bit of a communication dead end. You post your issue, I'll add it and the devs take a look at it and do what ever they do with it. Here, it's all about finding out what is causing the issue users are having.
It's unfortunate that I can't tell you what exactly is wrong but it could be any number of things that causes this and unless the bug behind it is identified, I don't think it makes much sense to have it in the bug forum.
Talking to the devs is a good way cause they might have come across it and can give you a way better answer then me.
Hope you understand what I'm trying to explain.