This is in the Stoneblock 2 modpack, haven't touched the config yet players have had cows naturally spawn even when the config file says they have a 0 spawn rate.

What type of cow? Fluid cows or vanilla cows?
If fluid cows:
Could u send cfg file (mc/config/fluidcows_v2.json) and what type cow spawned?
If not fluid cows:
Vanilla cows can spawn. Its not added by mod.

Ok. "Can spawn 0 cows."
Not really spawn any fluid cows by natural spawn.
Option with natural spawn activated only if 1 or more cows can spawn.
~
I think its Sponge bug.
Because if use only Forge - no problems with spawn.

Righto, might have to make a test server to see whats happening. Also while I have your attention, is there anything in game that speeds up their growth, like vanilla has for mobs e.g feed chicken seeds and it grows from a baby to an adult faster

Check breedingItemWork in config.
If true - u can speed up with wheat.
If false - only wait.
By default - false

Awesome, thanks for your help!

The cows that spawned? Fluid cows because that's why I posted the issue. Someone had an Infinity cow spawn apparently after a few others had fluid type had already spawned.

Do u use spigot?
Could u send cfg file (mc/config/fluidcows_v2.json) ?
Infinity cow spawned by natural spawn?

Fairly certain, they said it was their "5th natural spawned fluid cow"

fluidcows_v2.txt
Had to rename it to .txt to upload it here.
Spongeforge, not spigot.

Check in console "This is info! Support ... fluids. Can spawn ... cows.". What numbes in "..." in log?
And try without Spongforge.

[03:03:30] [Server thread/INFO] [fluidcows]: [FluidCows] This is info! Support 177 fluids. Can spawn 0 cows.

Spongeforge is the servers backbone and would break multiple things and with more than 20 players on at all times I won't be removing it sorry.