Ideas
Scorpio, could it also be linked to the wild prairie grass patches in the World of Chestnut Ridge? I notice each time I look up close to the area where there are those patches, my bag start to lag crazy... I did a test at some point and thread here, probably now archive unfortunately its lost in the void I think. But basically my sim could harvest up to 99+ prairie grass and so many collectibles, nectars etc... this was like a never ending task... I had him harvest it forever until it was completely done... I made him rich lol but its annoying for the lag mainly.
I've actually created a new thread for it and provided a demo with how it occurs and it's now under investigation. I'm not sure if it's linked to this issue or not, since it occurs even if there are no residential rentals in the area, but thought I'd mention it since you were the one to originally report it years ago. I experienced the same unbearable lag which is what prompted me to go searching to see if it was an issue.
You can remove the piles by uprooting the plan, using the destroy object cheat, or use SFS to edit the save file and delete them all at once (a bit convoluted and dangerous, but easier than hitting delete over and over since the grass respawns every time you load into the lot.)
[HR] Wild Prairie Grass Spawns Duplicating On Top Of Itself in Chestnut Ridge | EA Forums - 12286936