Now I know why I haven't been able to see the freezers in fridges ,I uninstalled the mod and yep freezers were showing up - it's a pity because I use this mod all the time.
I tested it both with IWBUMS and the latest release version with the same effect.
I do believe looking into sandbox there are options under "Advanced Zombie Options". Now the reason I bring up sandbox is because it would be ludicrous to think that the devs made up a separate, complex system for spawning zombies versus sandbox. ALSO NOTE that I am doing my best to understand this system made by the devs.
So the Sandbox Options menu shows many things, most notably in this screenshot you see "Population Peak Day" which in default (no settings touched) is Day 28. This means that the population is planned to be at it's peak by day 28.
To get there it takes a default number of zombies under "Population Multiplier", which to me is set to an unknown number. Let's say 1000. So because the setting is 1, it multiplies 100 by 1, which is 1000.
Then it checks "Population Start Multiplier" which is 1, so the population when you start is 1000 since (1000 x 1 = 1000)
"Population Peak Modifier" is how large the population will be on "Peak Day", which is now set to 1.5, so (1000 x 1.5 = 1500) means there will be 1500 zombies on day 28.
"Respawn Unseen Hours" dictates how long the game will take before it decides to check if they can spawn zombies in a cell (default 16 hours). This prevents you from leaving home for a quick raid and coming back to a few zombies in your house.
"RespawnHours" tells the game "Okay it has been they haven't been there in a while, respawn zombies there to start filling up the cell". Default is every 72 hours.
So when it wants to spawn zombies in a cell, it uses "Respawn Multiplier", which is set to 0.1 by default. So if there are 10 zombies chilling in a parking lot, you haven't been there for 16 hours, and it has been 72 hours since then, then it will spawn (10 zombies x 0.1 = 1 zombie) one zombies, making it 11 zombies chilling in a parking lot. I am NOT sure, but I would assume that if the result of the amount of zombies in a cell multiplied by Respawn Multiplier is less than 1, it rounds to 1 anyways unless it is 0 (explained next point)
However if you have 50 zombies in a parking lot, it now has 5. 100? Now 110.
Then the game thinks "Okay there are no zombies in this cell, and since RespawnMultiplier is set to 0.1, I can't spawn a zombie since 0 x 0.1 = 0" so it uses "Redistribute Hours" (default 12) to say "Okay every 12 hours I will take this group of zombies and lightly make them distribute into the other empty parts of the cell so I can eventually spawn zombies with Respawn Multiplier"
The rest of the option deal with grouping and travelling, which doesn't directly affect the numbers apart from "Move zombies so there are now 60 zombies inside this cell, spawn some zombies"
Once the total zombies calculated equals the population peak modifier, it will stop spawning zombies. However you are always killing zombies and zombies are moved around by meta events (ESPECIALLY the Helicopter),
So if you screw around with Population Multiplier, Population Peak Modifier and Population Peak Day you can have the game "evolve" by adding more zombies by default. This is also why exploring places in late game has them completely SURROUNDED by zombies instead of that 5 zombie group at the beginning.
Thanks. Nothing you can do to fix it at the moment, but will make sure RobertJohnson sees it.
If you start a new game .etc, you may want to back up your saves in %UserProfile%\Zomboid\saves\ until we can release a fix for it.