Sandbox variables are often used to set loot table values in mods. This works great the first time you create a game - but if you create a multiplayer game and update the sandbox settings this does not get updated in the game. The game does not seem to know that the sandbox settings have been updated until after distributions are done. If you check with the console on each distribution event you will see original sandbox settings, if you check in game, you will see updated ones.
This issue is located in the file: zombie/iso/IsoWorld.java #1665
Xyberviri explains it better on this forum: