This is my config

{
  "AirdropRate": 0,
  "Barrelcountdrop": 1,
  "BearRate": 100,
  "ScientistRate": 50,
  "WolfRate": 100,
  "ZombieRate": 100
}​

My understanding is that if I set the countdrop to 1, then it should have a chance at spawning anything at the very first barrel no?

Yes it should trigger on each barrel .
I tested it with 2 entitys at same time at 100 vallue and it spawned both.
i just took this plugin over but i will have a look at it

Merged post

Doing some testing and it spawned all entitys at once at every next barrel (ignore the chat colors it was the language file of the old version).
The way it workes in the algorytm it will trigger on each barrel but still has the random algorytm trying to get a random even when set at 100%.
So it sometimes skips a barrel.

Dont forget to reload the plugin after making some changes in its config.

Working on a update and checks to be released soon.