This is a cut and paste of my reply above but I figured I'd share it directly so you'll get a notification hopefully. This is working for me and another user mentioned the same.
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Hey everybody! Listen, I've got a workaround and it works every single time. I'm so relieved.
Here's what to do. Instead of clicking save, go to Manage Worlds. Then it's going to ask if you want to save. Click yes. That's all. Then just go back in and continue playing.
At first I wasn't sure it was working, so I changed my sim's outfit first and did it. When I went back in, sure enough she was wearing the same outfit I left her in so it did, indeed, save.
I hope this relieves you.