Z-level Bug? Zeds just appear from nothing

So after restarting the world 5 times i have bee getting a bug with doing a super city, 16 size and 0 space. Having Z levels on, i start with the shady basement start, I clear the basement, nothing down with me. i move around a bit, zeds are doing things up stairs, breaking windows, blowing up cars, you know zed things and out of the blue a LOT of zeds just appear in the basement with me, no door broken at the main stair case nothing, they just manifest from thin air.

Is anyone else having this issue? I have tried many times to replay this in other worlds and same thing happens each time. It is acting like they are grouping up too much and it forces them do the lower level.

Can confirm this happened to me too.

If hordes can travel between z-levels then that would probably be it. Last time I heard horde travel is unimpeded by terrain.

Heard that climbing code can’t tell between going up a level or down a level and zombies can climb down into a basement.

Are you folks sure they aren’t breaking through the floor? If it is noisy with lots of banging around. They probably chew their way through to get at you.

Smashing through Z levels is not something you or zombies can do.