Re: Sims 4 lag (2021)
@Daalia1 As long as Origin's CPU use stays low while you're playing, you don't have to worry about it. Having said that, 30% is a bit high, and you may be able to improve it by disabling a couple of services. Click Windows key-R, enter "msconfig" without quotes, click the Services tab, scroll down to the Origin Client Service and Origin Web Helper Service, and uncheck the box next to each one. Then restart your computer.
For the in-game lag, I'd like to know how your old saves run with no mods or custom content, or how your new saves run with all your mods and cc. (Or both, if you have the time to test.) The issue might be that your old saves are well-progressed, or it might be mods and cc, so testing them separately is crucial, especially since the problems don't show up immediately.
The error you're seeing is probably related to cc. It doesn't show up right away because you need to use the item(s) in question first, so if you made any changes between when your households would load and when they wouldn't, that's where to start looking.