Unknown command when using paramaters
Seems to add the spawns fine, but when I go to list them or start them, all i get is unknown command.  But if i just do /ss with no params, i get the help for the command, so it is loaded. 
What exactly did you write?

/ss "cavezombie1" start

and without ""

Unknown Command

You dont have to add the name there.

Use /ss <item|prefab> start

So if you added the "cavezombie1" as prefabs, just use:
/ss prefab start