Game won't save when I place "Clutter" items only

Background on mods: I've had Sims 4 for a while and never had this issue until recently despite the fact that all the mods I have (and have been using for years) are fully updated. I have a bunch of custom content in CAS but again, haven't downloaded any new stuff for years. I disabled my custom content and mods and this seemed to fix the issue, but I don't know how I'm meant to work out which mod/CC is causing it??

The issue: At first when I was building houses recently, I thought my game just had issues saving in general because I would go to save mid build and it would just keep loading and loading but not save. So, I tried saving after every single object I placed, and this mainly worked and it would save. However, I realised that after the placing of one specific object, the game would fail to save. This included things like the pile of two books, the sun cream, the open notebook, and the kitchen utensils pot. I've since done some experimenting and come to the conclusion that it is when I place an object that is in the "Clutter" category that my game fails to save. These are not custom content items, but normal Sims items. It is not an issue of there being too many items on the lot because I save before placing these Clutter objects and it fails to save immediately after. 

Zone objects: Also, I'm not sure if this is related, but it started around the same time. Every time I open Sims I get so many alerts come up asking if I want to delete zone objects, and I have thousands and thousands of these apparently. I press to keep them because I don't want to delete anything I don't want to, but perhaps this is contributing in some way? Is it safe to remove them?

Any help would be greatly appreciated! I really want to place my Clutter!