It's about generation bug. Or(hope not) about generation preview bug.
This seed (1249911531) shows fulgora vault both on 10 height and 9 height preview. BUT. In fact vault is not present on 9 cells version, though it WILL fit, because it's in the center of 10cell height.
I mean, if we remove either ...

Well, found this topic not to create new one about same problem.
It's rather not the issue about rebalance, it's about generation bug.
This seed (1249911531) shows fulgora vault both on 10 height and 9 height preview. BUT. In fact vault is not present on 9 cells version, though it WILL fit, because ...

okay. You mean, connection autoplace don't work cause of gates and therefore it's possible to put wagon so close?

https://imgur.com/a/8argTAS

You can place car with overlap if there is gates (maybe) on the way. Images - is how to reproduce bug.

If first car too close, nothing wrong happens.