Stacked Items Disappearing

I stacked a lot of objects while buildings a pantry, saved the game, and exited. When I returned, all (or most) of the stacked items were gone. Only the bottom item remained. Some of the items that weren't even stacked, but were placed beside each other using added slots, were also gone. I fixed it, saved, and left again. When I returned, some of the stacks were completely in tact, and others had the bottom item left. I tried saving the room to the gallery, leaving, returning, and placing the room from the gallery. Most of the stacked items stayed, but several of the items placed next to each other using added slots were completely gone. Not even the original remained. The ones that disappeared don't disappear when I exit the game, only when I place from gallery. 

I know stacked items disappear when you move walls and things like that, but I don't remember them disappearing when you exit the game. It's been a few years since I stacked stuff... still...

Someone on another forum said the game is coded that way. For the life of me, I can't imagine why the developers would do that.... And if it is the code.... wouldn't items placed on furniture also disappear??? It's the same slots...

Anyway... is there a way to prevent the items from being deleted? 

(What I mean by added slots: I went into sims4studio and added a slot on either side of the item... so it works similarly to the Dream Home Decorator shelves.... I've also had those disappear when I exited the game. And just like the clutter, some of the shelves stayed and other's didn't. Not sure if that still happens. I haven't really used them for a year or two.)