Lag in Sims 4 increasing over time

@biscuitist  When you save your progress without a pack present, that entire save should lose all data related to that pack.  Other saves would be unaffected.  Are you saying that in one single version of one save, you disabled Crystals, saved your progress, reenabled the pack, and you saw previous content from that pack?  That is not how things are supposed to work, and frankly it doesn't make sense from a data standpoint.

If that's somehow what's happening, it should be sufficient to load each played household without the pack present, then save once you're done.

Having said that, it doesn't sound like any particular pack is responsible for the majority of the save bloat.  You could disable all packs at once to see what happens (use "save as," of course), but it may be that nothing addresses the bloat in your current save.

The mod I recommended is fine; I just wanted to make sure you hadn't added anything else.  MCCC isn't necessary to catch the LE; it'll exist regardless.  And while MCCC is extensively tested, it's a large-enough mod that it's worth removing while troubleshooting just to keep things simple.

@puzzlezaddict That's exactly what I'm saying, yes! I've removed MCCC as you suggested, and have just disabled all packs except city living (I can move my household to a basegame world ofc, but I'm familiar with this lot), saved as a new file, re-enabled all the packs, and reloaded that save. Showers from the Komorebi pack are absent, but a dresser from the same pack has returned, as have garden items and floor textures. The closet from Get Together, a sofa from the maximalist kit, lights from Tiny Living, knitted items, things from all different packs that weren't there when I saved are back. In the household inventory there's someone else's bike, incense, game consoles, things from multiple packs. It looks completely random. There are also things in there I've never seen before, presumably bc they've been substituted. 

I've taken one of my nekkid bald Sims to another lot. Their pet cat is gone, but the litter box remains. There's no crystal tree this time, though.

Aspirations from my main household have reset as you'd expect, but when I've loaded into another household, although they are partially dressed, their previous aspirations haven't been altered. As far as I can tell, their furniture hasn't altered either. Only their cat has been deleted.

I don't know if this is symptomatic of the lag and/or bloat issues, but at this point, is there anything else to look at, or is it time to abandon it?

Thanks again

@biscuitist  This sounds like some serious data corruption, to be honest.  I can't say for sure because I don't have the tools to take apart a save, but I've seen other cases where progress is only incompletely saved.  Aside from the usual mod-related issues and the occasional game bug, this is typically a sign that the save itself is on its way out.  So while you could experiment for a little longer if you're motivated enough, I doubt you'd accomplish more than postponing the inevitable.

What you can do from here is save everything important to your in-game Library and place it in a new save.  MCCC or relationship cheats can restore relationships among sims in different saved households, and a money/freerealestate cheat can handle that side of things.  Please do check the new save file's size once you've set it up, and again after you've played for a sim-week or so, to make sure it's not bloating again.

Thanks again @puzzlezaddict , I appreciate your time and wisdom!

I've removed my households from the shared gallery, just in case they're cursed.

One last question A few more questions then, if I may! Since I'm too attached (weird, innit!) to abandon them, I'll take a few households into a new save. Do you think it safest to abandon the builds (and their photographs, sigh) and just bring in a few main households? If we're working on the assumption that data is corrupted, it's probably better to migrate as little as possible, right?

I'm not sure how to determine if the same thing is happening again, though. I can use save file size as an indicator, perhaps, but to begin with, if I bring in, say, a household of eight super-Sims, with their traits and whatever other data is preserved in the gallery, there's obviously no point in comparing the gallery size to a newly created household. I know I've asked this before, and it's impossible to give a straight answer, but what might be a guideline file size for a new save with, say, 6 households of eight intensively played Sims? Or a gallery file size for one such household? If I'm bringing in corrupted data to new game, I don't want to find out after another 3000 hours gameplay! What can I look for, to begin with?

@biscuitist  I don't think there's a good answer to how large your save should be.  I would be alarmed if the size increased rapidly, or if a new save (even with super sims and an equally-super mansion) was above... I'm not sure, maybe 40 or 50 MB?  It's hard to say with how much the game has changed over the years.

What I would do in your position is try the sims and the house(s) separately, maybe just letting the game clock run for a while as you do something else, and see what you get both for the initial size and the size after a sim-week or so.  If you want more data, you could also download other super sims and mansions from the Gallery and see how they behave.  I'd avoid older uploads since, again, the game has changed a lot, but anything post-For Rent would probably be fine.  Probably.

I wish I could give you a better answer, but this isn't really a science or even an art so much as voodoo.  On the plus side though, even in the unlikely event that none of your work is usable going forward, all you stand to lose is some time.  And it's worth keeping the sims or even the save on hand to test with future patches, in case something gets fixed in the future.

@puzzlezaddict No, that's a good answer! A guideline is always better than not having any clue.

So I'll do as you suggest, and hopefully rescue a few of my favourite Sims that way.

Thanks again for lending your time, knowledge, and assistance, appreciate it.