There are two possibilities I believe:
1.
All of your slabs's home story is the ground floor
, but it seems like they're on different stories in 3D. A building component can be on
any story while at the same time their location in 3D remains unchanged. For example, if your ground story is set to 9' tall, and you have a wall with an elevation of 0' place on the ground floor, its location will be the same with another wall placed on the second floor but with an elevation of -9' relative to home story. Although they're seemingly identical, their home stories are different. So I suggest you double check to see if your slabs are on the correct stories.
2. This isn't quite likely to happen, but if the above doesn't match your case check this:
The slabs may have been set to appear on the story above or below, but as I said it's not likely to happen automatically without your doing.