I had an invisible Sim just now for the very first time (at least for the first time that I noticed). I played a custom world (Riverblossom Hills) that initially ran way better than Bridgeport and started lagging around week 10. I slowed it down with Relativity to 50%, deleted trees and families and lowered the graphics settings but approaching week 13 even this could not help anymore. Time jumped in 5 minute intervals and everything was crawling. It took my Sim approximately 1 hour to get out of bed and make his way to the bathroom (in a 10x15 house). It was Saturday around midnight and I began to search for stuck Sims and "found" an invisible one (thanks to MasterController) that must have stood by the road for hours on end, because when I switched to his family he had the work-tone action in the upper left corner.
Resetting him fixed his invisibility and I ran a "reset everything" with MasterController and ran Overwatch cleanups twice. The lag persisted, however. I have a save, but as I said, it's in a custom world.
I also ran the program on my Mac that monitors CPU and memory usage and was quite surprised that my so-called mid-range machine was actually not working to its full capacity. The Sims used some 2 GB of RAM (out of 4) and there was still 1 GB left and the CPU only peaked occasionally at 75% (2.8 GHz Core 2 Duo), so no CPU overload and still enough RAM left.
I packed my family after that and will move it to another world. If the problem persits there, too, I'm done with that game.
EDIT: Iforgot to mention that by the time this whole disaster began I also experienced sudden jumps in save file sizes, like from 38 to 50 and then back to 38 MB.
